Morphological observations of Aulacoseira using scanning electron microscopy

Morphological observations of Aulacoseira using scanning electron microscopy

Peter A. Siver and Hedy Kling

Abstract: Despite the fact that the genus A~~lncoseirn Thwaites is a common component of phytoplankton communities in many North American water bodies, there are relatively few taxonomic based surveys utilizing the scanning electron microscope (SEM). In addition, based on the current literature, some species are difficult to identify or distinguish from other taxa. We present taxonomic and morphological observations on 19 taxa based primarily on collections made in Connecticut, U.S.A., and from central and northern Canada. Arllaco.seirn nttlbigrln (Grunow) Simonsen, A~rkc~coseit-el srlbarctica ( 0 . Miiller) Haworth, and Aulr~coseirn tet~elln (Nygaard) Simonsen were the most common species encountered in Connecticut, while Arllnco.seira islntlclica ( 0 . Miiller) Simonsen, Arllncoseirn grc~tzr~lnta (Ehrenberg) Simonsen, A. subarcticel, and A. clmbigrla were the dominant species from many central Canada localities. In the Canadian Shield region, specimens of the Aulncoseirn cli,stc~t~.s (Ehrenberg) Simonsen group, thc A~ilncoseirn lirnta (Ehrenberg) Ross in Hartley group, and Aulncoseirn perglabra (Oestrup) Haworth were more common. We had the most difficulty identifying taxa in the A. clistnns and A. pc7rglnbrc1 complexes and distinguishing A. lirnta from Aulncoseirn nlpigetla (Grunow) Krammer. The primary objectives of the paper were to provide an additional source of high-resolution SEM micrographs for many of the more common species of Aulncoseirc~, comment on the morphological detail of each taxon, and to discuss the difficulties we encountered using the current literature to identify some of the species. A few ecological observations are also provided. Lastly, we propose two new combinations, Aulncoseira p.seudontt~ericc~na (Camburn) comb.nov. and Arllncoseirn clistarls var. tzivaloides (Camburn) comb.nov.

Key ~vorcls: diatoms, Arllacoseirn, North America, taxonomy, n~orphology.

RCsurnC : Bien que le genre Ar~lncoseirr~ Thwaites soit une composante commune des communautCs de phytoplancton dans plusieurs milieux aquatiques de I'AmCrique du Nord, i l existe peu d'Ctudes basks sur la taxonomie qui utilisent la microscopic electronique par balayage (SEM). De plus, sur la base de la IittCrature courante, certaines espkces sont difficiles B identifier ou B distinguer de d'autres taxons. Les auteurs prkscntent les observations morphologiques ct taxonomiques de 19 taxons, b a s k s prioritairement sur des collections cffectuCes au Connecticut, U.S.A., et au centre ainsi qu'au nord du Canada. Les Au/c~co.seirc~ ntt~bigrm (Grunow) Simonsen, A~~le~coseirc~ sllbarcrica ( 0 . Miiller) Haworth et Arrlacoseirn tetlellc~ (Nygaard) Simonsen sont les espkces lcs plus friquentes au Connecticut, alors quc Ics Arrlacoseirn islatrclicc~ ( 0 . Miiller) Simonsen, A~llr~coseirn gmtlrtlnm (Ehrenberg) Simonsen, A. srlbarcticrr ct A. nttrbigrla sont les espkces doniinantes dans plusieurs IocalitCs du Canada central. Dans la rCgion du bouclier canadien, les specimens des groupes Aulc~coseira clistatls (Ehrenberg) Simonsen et Aulacoseirc~ lirnta (Ehrenberg) Ross in Hartley group, et du A~llncoseirn perglnbrn (Oestrup) Haworth sont plus frequents. Les taxons les plus difficiles B identifier ont CtC les espkces des complcxcs A. rlistntls et A. perglclbrc~; les espkces A. lirclta et Aulacoscim alpigetln (Grunow) Kramlner ont CtC difficiles a distinguer I'une de I'autre. L'objectif premier du travail consistait B fournir une source additionnelle de micrographies en SEM B haute rCsolution pour les cspkces les plus conlnlunes d'Aulacoseirc~, B commenter sur les spCcificitCs morphologiques dc chaque taxon, et i discuter les difficultts rencontrCes en utilisant la IittCrature courante pour identifier certaines espkces. Le auteurs prCsentent Cgalement quelques observations Ccologiques. Enfin, ils proposent deux nouvelles combinaisons, Aulncoseirn pse~tclomt~ericc~tc~ (Camburn) comb.nov. et A~~lncoseira dismtls var. t~ivnloides comb.nov.

Mots cl6s : diatoniCes, A~llncoseirn, AmCrique du Nord, taxonomie, n~orphologie. [Traduit par la redaction]

Introduction Despite the establishment of Aulacoseira many species con- sideied in the genus today were h i s t o r i c a ~ l ~ ~ ~ l ~ c e d in the

The genus Aulacoseira was Thwaites 848) genus Melosiro (see Krammer and Lunge-Bertalot 199 1). with Aulacoseira crenulm (Ehrenberg) Thwaites (Gallio- Simonsen (1979) reactivated the use of the name Aulacoseira nella Cre~ulata Ehrenberg) as the type et al. 1990). and moved the species of Melosira that possessed a collum

into it (~rarnrne; 1991a). Although most recent taxonomic Received October 16, 1996. works recognize the genus Aulacoseirn (e.g., Haworth 1988; P.A. Siver. Botany Department, Connecticut College. New Krammer 1991a, 1991b), a few have discussed the taxa London, CT 06320, U.S.A. under the genus Melosira (e.g., Florin 1981; Camburn and H. Kling. Freshwater Institute, Winnipeg, MB R3T 2N6, Canada. Kingston 1986). We recognize the transfer of taxa into the

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genus Aulacoseirn as proposed by Simonsen (1979) and followed by Round et al. (1990) and Krammer and Lange- Bertalot (1991).

Historically, classification of species within this genus relied primarily on the ratio of the mantle height to valve diameter, the orientation of the pervalvar rows of areolae, and details of the spines, especially separating spines (Krammer 1991~) . More recently, other characteristics, such as the morphology of the valve face, structure of the Ringleiste, shape of linking spines, and nature of the mantle areolae have also been considered important (e.g., Kobayasi and Nozawa 1981, 1982; Florin 1981; Camburn and Kingston 1986; Haworth 1988; Krammer 1991a, 1991 b). However, other features, for example the position of the rimoportulae, have not been fully utilized in the descriptions of species.

Until the recent works of Haworth (1988), Gronlund (1989), and Krammer (1991a, 1991b) who provided many excellent scanning electron micrographs (SEM), most taxonomic surveys of A~ilacoseira utilized primarily light microscopy (LM) to separate taxa. In addit&, except for the work of Camburn and Kingston (1986), there are few taxonomic works on this genus from North America. As part of a paleolimnological study of Connecticut lakes we often had difficulty identifying and quantifying some Aulacoseira with LM and understanding differences between taxa based on current literature. Gronlund (1989) also noted difficulty in identifying Aulacoseira. As a result, we relied heavily on SEM analysis for identification purposes. Diatoms have been utilized extensively in ecological and paleolimnological studies (e.g., Battarbee 1984; Charles 1985; Birks et al. 1990; Hall and Smol 1992; Cumming et al. 1992). Because species of Aulacoseira are almost always important components in such studies, especially from softwater localities (Cainburn and Kingston 1986), we decided to expand our study to include not only habitats from Connecticut, but also ones from central and northern Canada. The primary purposes of the current study are to provide ( i ) a set of SEM micrographs of many of the more important Aulacoseiln in North America; (ii) new morphological information on some species; and (iii) discussion of the difficulties we had in making our taxonomic distinctions.

Materials and methods

We have utilized the descriptions given by Krammer (1991~) of linking spines, separation spines, pervalvar costae, the collum, and Ringleiste for describing Aulncoseirn taxa. We found confusion in the literature concerning the use of the terms Ringleiste, sulcus, and pseudoseptum in this genus. According to Krammer (19910, p. 91) the Ringleiste is "either a solid ridge or a ring-like (annulate) wall, projecting inwards from the collum," and delimits the proximal position of the collum. Krammer ( 1 9 9 1 ~ ) further stated that the sulcus, a "small furrow" that separates the collum from the areolate mantle, was relatively deep in Aulocoseirn ccttibiglln (Grunow) Simonsen, but otherwise small or lacking in other species. We interpret Krammer's definition of a sulcus as referring to a groove on the external surface of the valve.

Haworth (1988, p. 139) stated "in most species of the genus Aulncoseiru, the structure that has previously been termed a sulcus is a solid ridge projecting inwards from near the margin of the mantle; it is not an inward fold of the silica wall, which is defined as a sulcus." The structure referred to by Haworth is obviously equal to the Ringleiste as defined by Krammer (1991cr), but clearly different than what Krammer defines as the sulcus. Haworth (1988)

further suggested that the Ringleiste be referred to as a pseudoseptum as defined by Ross et al. (1979), an idea clearly rejected by Krammer (1991~1). Round et al. (1990, p. 170) referred to the thickened ring of silica protruding to the inside of the valve at the "junction between the plain mantle edge and the areolate portion" as the Ringleiste, in agreement with Krammer. Round et al. (1990) further pointed out that the Ringleiste was hollow in A. arrlbigun. We have elected to refer to the thick inward ring of silica found at the junction of the collum and areolate mantle, including the hollow structure formed by A. ~ ~ ~ r ~ b i g r ~ i , as a Ringlcistc as discussed by Krammer (19910) and Round et al. (1990) and an external groove at the junction of the collum and aerolate portion of the mantle as a sulcus.

Phytoplankton tows, surface sediment, and sediment from lower sections of gravity cores were utilized in this study. In Connecticut, all three types of samples were examined for each of the 60 lakes studied by Canavan and Siver (1994). Similar types of saniplcs were also examined fro111 the Canadian lakes. A 10 pm mesh net was utilized to collect live samples during both warm and cold seasons. Sediment samples were either observed directly or after treatment with an acid-dichromate solution to oxidize the organic constit- uents (Battarbee 1986). For Connecticut samples, aliquots were air-dried on pieces of-alunlinunl foil, trimmed, mounted onto aluminum stubs with Apiezon wax, and coated with gold with a Polaron sputter coater (Siver 1987). For Canadian samples, aliquots were air-dried on glass coverslips. washed with distilled water, attached to aluminum stubs with double-sided tape, and coated with gold. Observations were made with either a Coates and Welter field emission (Connecticut) or a Cambridge 90s-100 (Canada) scanning electron microscope.

Results and discussion

Aulacoseira arnbigua (Grunow) Simonsen Melosira crenulatu var. ainbigua Grunow in Van Heurck Melosim ainbigua (Grunow) 0. Miiller

Cells of A. ainbigua consisted of valves that were most often longer than wide, possessed spiral pervalvar rows of areolae on the mantle, and had a relatively plain valve face (Figs. 1 - 12). The dimensions of cells were in agreement with Krammer and Lange-Bertalot (1991). In our specimens the height of the valve mantle was most often 1.5 to 3 times the diameter of the valve, however, valves with mantle height to diameter ratios less than one, and greater than five, were observed. Pervalvar rows of pores alternated with costae; each costae terminated at a spine. The mean number of areolae and pervalvar rows of areolae in 10 pm was 18. Areolae varied in shape from round to square, to less often elongate. Areo- lae with larger diameters tended to be square in outline and often had an internal reticulation of ribs (Figs. 7 and 9). A thin membrane, presumably organic in nature (Swift and Wheeler 1992), often covered the mantle areolae (Figs. 5-6 and 12). As the cell aged the remains of the membrane degraded and revealed the areolae (Figs. 5 and 9). The degree of curvature of the pervalvar rows of areolae ranged from slightly to strongly spiralled. If a pervalvar row of areolae was traced from the collum to the margin of the valve face it always spiralled to the right; we will refer to this character as a right-handed spiral.

Linking spines were triangular in shape and terminated each mantle costae (Figs. 7 and 9-12). The distal end of a linking spine was generally notched forming two forward- projecting lobes. The lobes were most often rounded (Figs. 7 and 9), although more acute or square-shaped lobes were also observed (Fig. 10). The distal notched end of each

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Figs. 1-6. Aulncoseira ambigun. Fig. 1. Filament with separation cell. Scale bar = 10 pm. Fig. 2. Filament depicting details of separation spines, mantle areolae, and the collum. Note that there is ca. one spine per mantle costae. Scale bar = 5 pm. Fig. 3. Linking cells. Note spiral arrangement of pervalvar rows of areolae and position of the rimoportula (arrow). Scale bar = 5 pm. Fig. 4. Filament with linking and separation spines. Scale bar = 5 pm. Fig. 5 . Filament depicting valves with different degrees of occlusion of mantle areolae. Note the right-handed spiral pattern of the mantle areolae (see text for details). Scale bar = 10 pm. Fig. 6. Cells depicting smooth valve face (left) and details of the shallow Ringleiste and rimoportula (arrow). Scale bar = 2 pm.

linking spine typically overlapped only a portion of the costae often possessed irregularly spaced siliceous knobs terminal-most areolae on the adjoining or sibling cell (Figs. 6, (Figs. 9 and 10). 10, and l l ) , causing the terminal-most row of areolae to Although some authors (e.g., Round et al. 1990) had sug- refract light differently from unobstructed areolae on the gested that A. atnbigua lacked separating valves, Kobayasi mantle when viewed with light microscopy (LM). Mantle and Nozawa (1981) and Le Cohu (1991) clearly demon-

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Figs. 7-12. Aulacoseircr ambigun. Fig. 7. Close-up of valve face with linking spines. Scale bar = 2 pm. Fig. 8. Close-up of the specimen in Fig. 1 depicting the valve face with separation spines. Note the peripheral ring of areolae. Scale bar = 2 pm. Fig. 9. Close-up of linking spines with shallow notches. Note that the thin covering over the areolae is beginning to degrade on the lower, but not the upper, cell. Scale bar = 1 pm. Fig. 10. Close-up of linking spines with deeper notches and more angular lobes. Scale bar = 1 pm. Fig. 11. Close-up of linking spines connecting valves where the areolae are still covered with a thin siliceous layer. Note how the spines only partially overlap the terminal-most areolae of the adjacent cell. Scale bar = 0.5 pm. Fig. 12. Close-up of a filament depicting the arrangement of small siliceous bumps and position of a large rimoportula (arrow). Scale bar = 2 pm.

strated the occurrence of both linking and separating valves of A. ambigua were pointed, equal in length, and terminated for this taxon. Although rare, we were also always able to the ends of each pervalvar mantle costae. find separating valves (Figs. 1, 2, and 8). Separating spines The valve faces of most A. ambigua specimens, especially

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valves with linking spines, were smooth and lacked pores (Figs. 6 and 7). However, separating valves often had a single ring of areolae on the valve-face margin (Figs. 4 and 8). Each valve commonly possessed at least one elongate rimoportula located at the end of a row of mantle areolae next to the collum (Figs. 1, 3-6, and 12). Wider cells, especially those formed immediately after initial cells, often had at least two rimoportulae. Despite the large range in the mantle height to valve diameter ratio, the height of the collum was remarkedly stable. The collum was often ornamented with small siliceous knobs. The Ringleiste was shallow and relatively thick, in agreement with Krammer and Lange-Bertalot (1991) (Figs. 2 and 6). In accordance with other authors we found that the Ringleiste of this species was hollow (e.g., Kobayasi and Nozawa 1981 ; Round et al. 1990). In LM a distinct U-shaped "sulcus" could be readily observed, which is often viewed as characteristic of this species (Kobayasi and Nozawa 198 1; Krammer 199 la, p. 9 1 ; Krammer and Lange- Bertalot 1991). However, based on our SEM observations, it is clear that the feature viewed with LM is not a U-shaped indentation of the outside of the valve, or sulcus, as stated by Krammer (1991~) . More likely, the U-shaped structure viewed with LM is the outline of the thick and hollow Ring- leiste. An excellent study of the morphology of girdle bands and auxospore formation is provided by Le Cohu (1991).

Aulacoseira ambigua was the most common and widespread species of Aulacoseira in Connecticut lakes, especially in mesotrophic and eutrophic waterbodies. It was, however, distinctly less abundant in both oligotrophic and the most eutrophic conditions. Aulacoseria ambigua was most often observed during overturn periods in Connecticut lakes but rarely found with Aulacoseira granulata (Ehrenberg) Simonsen, a rare taxon in Connecticut lakes. In Canadian prairie lakes A. ambigua was also common, often found in shallow, moderately nutrient-rich lakes during periods of mixing and lower light levels. In the Canadian prairie lakes it was also commonly observed with Aulacoseira islandica ( 0 . Miiller) Simonsen in the spring after ice out, and coexisted with A. granulata during summer. In larger Canadian Shield lakes it was often a codominant during spring.

Aulacoseira subarctica ( 0 . Muller) Haworth Melosira italica ssp. subarctica 0. Muller Aulacoseira italica ssp. subarctica ( 0 . Miiller) Simonsen

A wide range in the mantle height to valve diameter ratios was observed in populations of A. subarctica (Figs. 13 -22). Most populations consisted of valves with ratios close to 2: 1, however, frustules with ratios ranging from 0.5 to over 3 were also observed (e.g., compare Figs. 17 and 22). Jewson (1992) also found a wide range in the diameters of valves but noted that over 90% of frustules in Lough Neagh, Northern Ireland, were within a small range in valve diameter because of processes that preferentially removed both narrow and broad valves. The mantle areolae are most often round in cross section and positioned in right-handed spiral pervalvar rows (see above). As the mantle height to valve diameter ratio decreases the mantle areolae often become aligned in more diagonal or straight rows (Fig. 15). Mantle areolae are often spaced a similar distance from other neighboring areolae within the same pervalvar row as they are from neighboring pores in adjacent rows. Thus, for a given valve,

the number of areolae and the number of pervalvar rows in 10 pm was similar; the mean for our populations was 18, in close agreement with Haworth (1988) and Krammer and Lange-Bertalot (199 1). The mantle areolae are aligned in a straight, diagonal, or sometimes irregular manner around the mantle circumference.

We observed only separating spines in the many collections of this species (Figs. 13-22). Each spine arises from the coalescence of two costae along the upper portion of the mantle. The costae form a substantial and thick base that support long, acutely tapered and pointed spines of equal length. The terminal portions of the spines are positioned in grooves on the mantle of adjacent cells in such a way that the spine tips become aligned with the pervalvar rows of areolae situated between the coalesced costae (Figs. 17 and 18). The areolae between the two coalescing costae often fuse and become elongate in shape (Figs. 17 and 21). As is common with other species of Aulacoseira the mantle costae often possess a single row of rounded siliceous knobs; the knobs also become fused along the terminal portion of the spine producing a thickened ridge (Figs. 17 and 18). Although rare, we have observed spines formed by the coalesence of three mantle costae (Figs. 17 and 18, arrow). To our knowl- edge only separating spines have been described for this taxon (e.g., Haworth 1988; Jewson, 1992). Only one other species, ~ulacoseira herzogii (Lemm.) ~imonsen, has been characterized as having only separation spines (Jewson et al. 1993). However, we have recently observed a collection of cells from MacDonald Lake in Australia supplied to us by Glenn McGregor (University of Queensland, Brisbane, Aus- tralia) that possessed separating spines typical of A. subarctica and linking spines similar in morphology to those of A. ambigua (unpublished data). Further observations are needed to assess if this population is indeed A. subarctica.

The structure of the valve face varied. The most common morphology was a smooth valve face with a single ring of relatively large pores positioned on the periphery. Each pore in the peripheral ring was radially aligned with and positioned adjacent to a spine; pores were lacking between the spines (Figs. 14 and 20). Additional rings of pores located to the interior of the peripheral ring were sometimes found on larger specimens with small mantle height to valve diameter ratios (Fig. 19). The pores of the inner ring were usually radially aligned between the spines, and thus alternated with those of the peripheral ring. Additional inner rings of pores were often incomplete and more random in nature. A few specimens had other randomly placed pores on the valve face.

The height of the collum varied but was most often quite narrow. A; discussed by Jewson (1992), stepped valves (Fig. 14) were commonly observed. The Ringleiste was thick, solid, and varied between extending only slightly inward (Fig. 22) to extending inward about one quarter to one half of the radius of the cell (Fig. 21). In general, the distance that the Ringleiste extended inward was inversely related to the mantle height to valve diameter ratio. At least one rimoportula was positioned at the collum end of a mantle striae (Fig. 22).

In Connecticut lakes, A. subarctica was commonly observed in more oligotrophic waterbodies during the spring and less often in the fall. In populations from Canadian arctic and shield lakes this taxon was observed forming auxospores under

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Figs. 13-18. Aulacoseira subarcrica. Fig. 13. Two-celled filament. Scale bar = 10 pm. Fig. 14. Two valves with different mantle height to valve diameter ratios. Note the right-handed spiral arrangement of the mantle areolae and the relatively smooth valve faces. A step on the mantle can be seen on the valve on the left. Scale bar = 5 pm. Fig. 15. Close-up of a valve depicting spine morphology. Note coalescence of two mantle costae to form each spine. Scale bar = 2 pm. Fig. 16. Valve with a large mantle height to valve diameter ratio and relatively thick spines. Scale bar = 5 pm. Fig. 17. Close-up of spines connecting two valves. Note the elongated areolae a[ the bases of the spines resulting from the coalescence of several areolae, the details of the collum, and the costae spanning three mantle costae (arrow). Scale bar = 2 pm. Fig. 18. Spines connecting two valves. Note that all but one spine span two mantle costae; the spine depicted by the arrow spans three mantle costae. Scale bar = 1 pm.

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Figs. 19-22. Aulncoseirn subnrctica. Fig. 19. Valve with a short mantle height to valve diameter ratio. Note areolae arrangement on the valve face. Scale bar = 2 pm. Fig. 20. Valve depicting the most common valve face morphology. Note the peripheral ring of areolae aligned with the bases of the spines. Scale bar = 2 prn. Fig. 21. Relatively short valve with a relatively wide Ringleiste. Scale bar = 2 pm. Fig. 22. Long valve with a smaller Ringleiste than that in Fig 21. Note the position of the rimoportulae (arrow). Scale bar = 5 prn.

the ice in the spring. In the smaller Connecticut lakes it often coexisted with Cyclotella species, whereas in the larger Canadian Shield lakes it was often found with A. islandica and A. ambigua.

Aulacoseira granulata (Ehrenberg) Simonsen Melosira granulata Ehrenberg

The mantle height to valve diameter ratio ranged from 1.5 to approximately 3.3, with a mean of 2.5 (Figs. 23 -28). The areolae on the mantle were large, coarse, most often square in outline, and aligned in either straight or right-handed spiral pervalvar rows. It was common for rows of areolae to be straight on separating valves (e.g., Figs. 24, 26, and 27), but curved on linking valves (e.g., Figs. 25 and 28), yielding a distinct dimorphic character. On many specimens a series of ribs was evident within each areolae (Fig. 25). The valve face was smooth and lacked areolae; however, on separating valves isolated areolae were observed on the periphery of the valve face at the base of the spines (Fig. 26). Cell dimensions were in agreement with Krammer and Lange-Bertalot (1991).

Both separating and linking spines were present. Linking

spines are similar in morphology to those of A. ambigua (Figs. 25 and 28). Separating spines are sharply pointed, range in length from 2 pm to almost the length of the valve, and result from the coalescence of two mantle costae (Figs. 26 and 27). The height of the collum ranged from 1.3 to 2.2 pm, with a mean height of 1.7 pm, and was ornamented with small siliceous knobs (Figs. 27 and 28). On most valves a rimoportula was situated close to the second or third row of areolae from the collum (Figs. 24, 25, 27, and 28). An additional rimoportula was sometimes observed on the mantle near the valve margin (Fig. 27, lower arrow). The Ringleiste (not shown) was shallow.

Small specimens may be hard to separate from those of A. ambigua, especially if separating spines are not present. In addition to separating spines, the coarseness of the areolae and position of the rimoportula can also be used to differen- tiate between the two taxa. Populations of A. granulata were rare in Connecticut lakes, found only in several highly eutro- phied localities. It was a more common taxon in eutrophic prairie lakes and rivers in Canada during the summer, especially under light-limited turbid conditions.

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Figs. 23-28. Arrlacoseira granrrlata. Fig. 23. Filament with a separation valve possessing parallel rows of areolae on the mantle and connecting valves with wavy rows. Scale bar = 5 pm. Fig. 24. Intact separation cells with irregularly sized spines and straight rows of large areolae. Arrow depicts position of rimoportula. Scale bar = 5 pm. Fig. 25. Long and narrow connecting valve with curved rows of mantle areolae. Note the reticulated nature of each areolae. A rimoportula is positioned in the second row of areolae from the collum (arrow). Scale bar = 1 pm. Fig. 26. Frustule with irregular sized separation spines and a smooth valve face except for the areolae positioned at the base of the spines. Scale bar = 5 pm. Fig. 27. Separation valve with a rimoportula within the spine groove (arrow) spaced about two areolae from the collum. A second rimoportula can be observed on the mantle near the juncture with the valve face (arrow). Note the large square shaped areolae arranged in straight rows. Scale bar = 5 pm. Fig. 28. A filament of A. arnbigua (left) and A. grarzulata (right). Note the difference in the coarseness of the areolae and in the relative positions of the rimoportulae (arrows). Scale bar = 5 pm.

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Aulacoseira islandica (0 . Muller) Simonsen Melosira islandica 0 . Muller Aulacoseira islandica ssp. helvetica ( 0 . Muller) Simonsen Aulacoseira skvortzowii Edlund, Stoermer, & Taylor

The morphological variability of A. islandica has been discussed in detail by Stoermer et al. (198 1 , 1985), Genkal et al. (1986), Genkal and Popovskaya (1991), and Le Cohu (1996). In our collections, filaments were either isomorphic or polymorphic with respect to the pattern of areolae, spine type, and position of the rimoportulae (Figs. 29-41). A greater degree of polymorphism was observed within populations found in open water than those under the ice. In general, the mantle areolae were small and quite fine in nature, and positioned parallel to the pervalvar axis (Figs. 34, 35, and 39). Areolae were, however, polymorphic in nature ranging from being circular (type 1 in sense of Stoermer et al. 1981) to slitlike (type 2) or consisting of multiple (usually two) sets of pores (Figs. 30, 32, 33, and 36). The different types of areolae were found on the same filament (Fig. 38). The multiple-pored mantle areolae were often unorganized or in curved rows, especially near the collum (Fig. 30). The number of areolae and rows of areolae per 10 pm were in agreement with those observed by Genkal and Popovskaya (1991). The complexity of the velum associated with each areolae was recently discussed by Le Cohu (1996).

Both linking (Figs. 32-34, 36, and 39) and separating (Figs. 30, 35, and 38) spines were observed. Linking spines terminated each mantle costae and were spatulate or dog boned in shape (Figs. 34, and 36). Separating spines were equal in length, relatively short, pointed, and also terminated each mantle costae (Figs. 35, and 38). Populations observed under an ice cover possessed primarily linking spines, resulting in very long chains up to 1.7 mm in length. However, chains of cells observed during open-water periods commonly formed separating valves resulting in a much shorter mean chain length.

The valve face was punctate with areolae that were morphologically similar to those found on the mantle (Figs. 30 and 3 1). Valves possessed multiple rimoportulae positioned along the Ringleiste (Fig. 40) and on the mantle (Fig. 41); a similar finding was noted by Le Cohu (1996). The Ring- leiste usually protruded only a short distance into the cell, was relatively thick, and was solid in nature (Fig. 40). Speci- mens lacked a sulcus (Fig. 36); however, as noted by Le Cohu (1 996), stepped valves were commonly observed (Figs. 35, 36, 38, and 39). The step on the mantle was positioned approximately five (Fig. 35) to eight (Fig. 36) areolae from the valve face. We also observed frustules with a step on each valve (Fig. 38) as described by Jewson (1992) for A. subarctica.

According to Krammer and Lange-Bertalot (199 1) A. islarz- dica could be confused with A. crenulata (see below), which also possesses rows of areolae that are parallel to the pervalvar axis. However, A. crenulata has linking spines that are more robust in size and structure, and areolae that are often elongated in shape (Figs. 46 and 47). Recently, Edlund et al. (1996) described a new species, A. skvortzowii, from Lake Baikal, Russia, that had been previously identified as a number of different taxa, including A. islandica and A. islandica ssp. helvetica. The separation of A. skvortzowii from

A. islandica is based primarily on the ability of the former species to form true resting spores. Although we have not observed resting spore formation in A. islatzdica, we do not believe that there is any significant difference between the valve morphologies of A. islandica and A. skvortzowii.

Specimens of A. islandica were observed only from sites in Canada and were lacking in all of the live and sediment samples from Connecticut. AS has been observed by Kozhova et al. (1982) and Genkal and Popovskaya (1991) for large Russian lakes, A. islatzdica was common in large arctic and temperate Canadian lakes, where it formed substantial populations in late winter under the ice and was often a common element of the spring bloom.

Aulacoseira italica (Ehrenberg) Simonsen Melosira italica (Ehrenberg) Kutzing Gallionella italica Ehrenberg

Our observations of A. italica are based on only three rare populations. Specimens had a diameter between 13 and 17 pm and a mantle height to valve diameter ratio of approximately 1 (Figs. 42-45). Mantle areolae were large, mostly circular, and aligned in distinctly right-handed spiraled rows. Linking spines were large, spatulate in shape, and terminated with many small fingerlike projections (Figs. 44 and 45). In addition, spines had a row of circular but flat, siliceous knobs (Figs. 44 and 45). Although the true nature of the connection between the pervalvar mantle costae and spines was not visible because of the close interlocking nature of the spines, there were approximately two costae per spine. The collum possessed many small siliceous knobs (Fig. 43), and all specimens had a well developed Ringleiste (Fig. 42). Kobayasi and Nozawa (1981, 1982) found that the Ringleiste of this species was solid but shallower than those found on our specimens. Like Kobayasi and Nozawa (1982), we did not observe separation spines, nor the structure of the valve face.

Haworth (1988) suggested that A. italica was conspecific with Aulacoseira valida (Grunow) Krammer, an idea that Krammer (19916) strongly disagreed with. According to Krammer (19916) an important difference between the two taxa is that linking spines of A. italica arise from a single pervalvar costae, while those of A. valida arise from two costae. Despite this difference, the specimen of A. italica depicted by Krammer (19916, Fig. 44) also had approximately two mantle costae per spine, like our specimens. Based on our evaluation we believe that the differences between these two species need further examination.

Aulacoseira crenulata (Ehrenberg) Thwaites Gallionella crenulata Ehrenberg Melosira orichalcea sensu Ralfs Melosira crenulata (Ehrenberg) Kutzing Melosira italica f. crenulata (Ehrenberg) 0 . Muller

Although we did not observe populations of this taxon in our localities, we have included a few observations from a cul- ture provided by David Czarnecki (Loras College, Dubuque, Iowa). Specimens had rather long spatula-shaped linking spines similar to those of A. italica but lacked the many fine fingerlike projections (Figs. 46 and 47). The primary characteristic that we used to distinguish this species from

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Figs. 29-35. Aulacoseira islandicc~. Fig. 29. Filaments from a bloom under 1.2 m of ice at Berens River. Lake Winnipeg, Canada. Relatively uniform morphology with cells consisting of fine structured. type I valves. This morphotype is often identified as A. islarzdicrr ssp. helvetica Muller. Scale bar = 25 pm. Fig. 30. Separation valve with small, evenly sized spines and a punctate valve face. Note most areolae consist of double sets of pores. Scale bar = 1 pm. Fig. 31. Connecting valves depicting the dog-bone shaped spines and the punctate valve face. Scale bar = 2 pm. Fig. 32. A very thin walled frustule with parallel rows of double areolae and relatively long connecting spines. Scale bar = 1 pm. Fig. 33. Close-up of connecting spines. Note that a spine terminates each costae. Scale bar = 1 pm. Fig. 34. Connecting cells with areolae consisting of a single circular pore. Note the parallel arrangement of the rows of areolae. Scale bar = 1 pm. Fig. 35. Separating cells with circular shaped areolae in parallel rows. Note step on the mantle. Scale bar = 2 prn.

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Figs. 36-41. A~ilacoseira islandica. Fig. 36. Linking valve with double sets of pores, many of which are elongate in shape. Note step on the mantle. Scale bar = I pm. Fig. 37. Close-up of girdle bands. Note valves are polyn~orphic with respect to areola type. Scale bar = 2 pm. Fig. 38. Filament with both linking and separating spines and valves with different areolae structure. Note there is a step on the mantle of each valve. Scale bar = 5 pm. Fig. 39. Linking valves with straight rows of small, mostly circular-shaped areolae. Note step on the lower valve. Scale bar = 5 pm. Fig. 40. Inside view of the solid Ringleiste and position of two rimoportulae (arrows). Scale bar = I pnl. Fig. 41. Inside view depicting positions of four rimoportulae scattered along the mantle. Scale bar = I pm.

A. italica was thal the mantle areolae were fine, elongated, The organism was isolated from a calcium-rich locality, and in straight rows. It appears that this taxon is relatively which is in agreement with observations made by Krammer common in Iowa (D. Czarnecki, personal communication). and Lange-Bertalot (1991) for this species.

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Figs. 42-45. Aulacoseira italicu. Fig. 42. Filament showing right-handed spiral arrangement of mantle areolae. Note the large Ringleiste. Scale bar = 10 pm. Fig. 43. Cell with large spatula-shaped linking spines. Note the large mantle areolae and the structure of the collum. Scale bar = 5 pm. Figs. 44 and 45. Close-ups of linking spines. Note the series of small fingerlike projections and the row of circular, flat knobs. Scale bars = 2 pm. Figs. 46 and 47. Aulacoseira crerzuluta. Cells with relatively small, elongate mantle areolae in straight rows. Note the large spatula-shaped linking spines. Scale bars = 2 pm (Fig. 46) and 5 pm (Fig. 47).

Aulacoseira perglabra complex

Aulacoseira perglabra (Oestrup) Haworth Melosira perglabra Oestrup Melosira lirata var. perglabra (Oestrup) Florin Melosira excurrens Nygaard

Aulacoseira perglabra var. jloriniae (Camburn) Haworth Melosira perglabra var. floriniae Camburn

Most of thes~ecimens that we observed within this c o m ~ l e x were A. perglabra var. perglabra; however, we had several specimens that were difficult to assign to one of the varieties based on current literature descriptions. In an attempt to

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Figs. 48-53. A~llncoseirn perglabra var. perglabra. Figs. 48-52 are views of the same specimen. Fig. 48. Valve depicting both valve and mantle views. Scale bar = 10 pm. Fig. 49. Valve view. Note the arrangement of pores on the peripheral region of the valve. The peripheral-most ring consists of elongate pores, while the inner ring is composed mostly of circular-shaped areolae. Scale bar = 2 p n ~ . Fig. 50. Close-up of the peripheral region of the valve. Note that there appears to be a third ring of valve areolae that are still closed with a siliceous covering. Scale bar = I pm. Fig. 51. Close-up of mantle region showing thc positions of the spines on the buttresses. Note that the grooves between the buttresses are only partially opened. and that the buttresses arc still fused at the top. Scale bar = I pm. Fig. 52. Close-up of the peripheral region of the valve. Note the connection between the elongated peripheral areolae on the valve and the slits within the grooves on the mantle. Scale bar = 1 pm. Fig. 53. Close-up of the arrangement of spines connecting two valves. Scale bar = 1 pm.

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Can. J . Bot. Vol. 75, 1997

better understand the two varieties we examined Camburn type material of A. perglabra var. floriniae provided to us from Paul Hamilton (Canadian Museum of Nature, Ottawa, Ont.). We will discuss our findings in the following order. First, we will describe the features of our specimens of A. perglabra var. perglabrn. Second, we will review the differences between the two varieties based on the current literature. Third, we will discuss our observations of specimens from the type material. Lastly, we will discuss the problematic specimens in our collections and discrepancies with the current literature.

Cells from our collections of A. perglabra var. perglabm were characterized by a lack of areolae on the mantle, a very small mantle height to valve diameter ratio, a valve face with areolae restricted to the peripheral region, and distinctive spines that were positioned on buttresses that extended along the mantle (Figs. 48-54). Our specimens had two or three rings of areolae positioned on the periphery of the valve face. Areolae in the peripheral-most ring were located between the spines, radially elongate, and often extended down the mantle (Figs. 49 and 52). We often observed several smaller areolae within each elongated areola. The areolae of the inner valve-face rings were generally circular or only slightly elongate in shape (Figs. 49 and 52); some were often covered with a membrane (Figs. 50 and 52). The areolae on the periphery of the valve face were not in radially aligned rows, and the center of the valve face often had small bumpy knobs. Valve-face areolae were sometimes (Figs. 55-57), but not always (Figs. 61 and 63), occluded on the interior of the valve by vela; it is possible that the vela were degraded on some specimens (Likhoshway et al. 1992).

The peripheral row of areolaeon the valve face were con- nected to the elongated openings positioned between the spine buttresses on the mantle (Figs. 51 and 52). The degree to which the connection could be observed was deuendent on whether the thin siliceous coverings between the buttresses had opened or not (Figs. 5 1, 52, and 54). For example, in Figs. 51 and 52 you can view into the elongated valve face areolae and through the slits between the buttresses. How- ever, in Fig. 54 although the internal connections are still present, they can't be viewed because the thin siliceous coverings between the buttresses are not opened.

On our specimens of A. perglabra var. perglabra spines were long and narrow, slightly constricted near the base, somewhat flat in cross section, and tapered to either a point or a small anchorlike structure (Figs. 48-56). Each spine was positioned on a buttress that continued well onto the mantle. Spines with less of a taper were observed on the same specimens with tapered spines. We observed a slight or no Ring- leiste (Figs. 55, 57, and 63). On our specimens a structure that we believe to be a rimoportula was often found at the collum end of the mantle ( ~ i g . 57, insert). Some specimens of type material from McMearney Lake, Michigan (see below), appeared to have a rimoportula close to the junction of the valve face and mantle (Fig. 63).

The arrangement of areolae on the valve face and the degree to which the peripheral-most ring of areolae extend onto the mantle are important features used to separate A. perglabra var. floriniae from var. perglabra (camburn and Kingston 1986). According to the original description by Camburn and Kingston (1986), there is a single ring of

areolae on the periphery of the valve face of A. perglabra var. floriniae. The areolae of the peripheral ring are regularly spaced, radially aligned, and extknd only a short distance onto the mantle. As noted above, there are multiple rings of areolae on valves of A. perglabra var. perglabra and the areolae are variable in shape, distribution, and orientation. In addition, Camburn and Kingston (1986) stated that the peripheral ring of areolae on the valve face and the buttresses extended farther down the mantle on A. perglabra var. perglabra than on var. florkziae. Florin (Camburn and Kingston 1986, p. 32) did not agree that the two varieties represented morphologically distinct taxa. In addition, although Haworth (1988) transferred var. floriniae, she stated that "there is such a gradient in forms found in Cumbrian waters that it is impossible to separate A. perglabra var. floriniae . . . from the nominate form."

Our examination of material from McNearney and Cusino lakes revealed many specimens of A. perglabra var. perglabra (Figs. 60-63), and a few of A. perglabra var. floriniae (Figs. 64 and 65). The specimens that we considered var. floriniae possessed a single peripheral ring of elongate areolae on the valve face (e.g., Fig. 65) as described by Camburn and Kingston (1986); in our opinion these specimens had a mantle structure similar to that described above for var. perglabra. A rimoportula was observed on the specimens of var. floriniae in a similar position as in many of our specimens of var. perglabra (Fig. 64).

The arrangement and shapes of areolae on the valve faces of most of the specimens from our collections were clearly consistent with those of A. perglabra var. perglabra and not A. perglabra var. floriniae. As noted by Camburn and Kingston (1986), distinguishing between the two varieties based on characteristics of the mantle is very problematic. Our specimens always had grooves on the mantle between the spine buttresses, but the degree of the opening of the thin membrane covering the grooves varied. We observed specimens where the openings between the buttresses were closed, partially opened, or totally opened. Valves lacking openings between buttresses (Figs. 55 and 56) have not been previously reported for either taxon. We believe that the degree to which the grooves are opened may simply be related to the age and condition of the cell. Based on our observations, and as reported by Haworth (1988) and Florin (Camburn and Kingston 1986, p. 32), we are of the opinion that there is a considerable degree of overlap between A. perglabra var. perglabra and A. perglabra var. floriniae, especially regarding the characteristics of the mantle.

We observed several problematic specimens in our collections that possessed spines on buttresses that alternated with grooves that extended a short distance onto both the mantle and the valve face but lacked additional rings of areolae on the valve face (Figs. 58 and 59). The grooves appeared to be occluded by vela, and the spines had numerous small lateral extensions. Although we are uncertain of the identity of these specimens, we do feel that they may be within the A. perglabra complex. We also observed a few specimens from one Connecticut lake that had a peripheral ring of areolae on the valve face that were radially aligned with grooves on the mantle situated between the spines, similar to what has been described for A. perglabra var. floriniae by Camburn and Kingston (1986). However, these specimens differed in

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Figs. 54-59. Aulacoseircr perglabra complex. Fig. 54. Valve with three peripheral rings of valve areolae and closed grooves between the mantle buttresses. Scale bar = 5 pm. Fig. 55. Inside view of a valve lacking openings along the mantle. Scale bar = 2 pm. Fig. 56. Close-up of the specimen in Fig. 55 depicting details of the mantle. Scale bar = 1 pm. Fig. 57. Close-up of the specimen in Fig. 55 depicting the areolae covered by vela. Note the lack of any noticeable Ringleiste. Insert is of another specimen depicting the position of a rimoportula. Scale bar = 1 pm. Figs. 58 and 59 are of the same specimen that we believe is within the A. perglabrci complex. Note the spines positioned on buttresses that alternate with grooves that extend onto the mantle and the lateral projections on the spines. Scale bars = 5 pm (Fig. 58) and 1 pm (Fig. 59).

always possessing large pores on the mantle below approxi- Camburn and Kingston (1986) discussed the idea that the mately every fourth groove; this feature has never been taxon identified by Renberg (1976, Plate 4, Figs. 20-2 f ) as reported for any taxon of A. perglabra. Melosira fennoscanrlica was identical with A. perglabra var.

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Figs. 60-65. Aulacoseircl perglabra var. perglabra (Figs. 60-63) and A. perglabrcl var. Joritliae (Figs. 64 and 65). Specimens from type material of A. perglabrcl var. Joritliae from McNearney Lake. Michigan, U.S.A. (see text for details). Fig. 60. Valve view showing only partial development of the second peripheral ring of areolae. Scale bar = I pm. Fig. 61. Ins~dc vicw of specimen. Scale bar = I pm. Fig. 62. Valve with three peripheral rings of areolae. 'There appear to be additional areolae on thc valve face that are covered with thin membranes. Scale bar = 1 pm. Fig. 63. Inside view of a valve with three peripheral rings of arcolac. Arrow depicts position of a rimoportula. Scale bar = I pm. Flg. 64. Inside view showing two rings of areolae still partially covered by vela. Arrow depicts the position of a rimoportula. Scale bar = 1 pm. Fig. 65. Valve with only one peripheral ring of elongated areolae that extends along the mantle. Scale bar = 1 pm.

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jloriniae. It is clear that our specimens of A. perglabra var. perglabra are the same as those described by Haworth (1988) and Camburn and Kingston (1986) but differ from the organism described as A. perglabra by Krammer (199 la). Accord- ing to Haworth (1988) and Camburn and Kingston (1986), A. perglabra was originally depicted by Oestrup in 1910 as Melosimperglabra and pictured in Florin (1981) as M. lirata var. perglabra. However, Krammer (1991~) stated that the description of A. perglabra made by Haworth (1988) did not conform to material on Oestrup's original lectotype slide. Krammer (1991~) further described A. perglabra as having a very low mantle height to valve diameter ratio of 0.24- 0.35, an areolate valve face, mantle striae consisting of two or three areolae, and short pointed spines that alternated with large peripheral valve-face areolae (Krammer 1991a; Krammer and Lange-Bertalot 1991). In our opinion the taxon described and pictured by Krammer and Lange-Bertalot (1991, Plate 33, Fig. 13) is similar in many respects to A. distans var. tenella but differs in having a wide Ringleiste and linking spines that each span two pervalvar costae. Since we did not observe the original material of Oestrup, we can offer no solution to the apparent differences in the literature surrounding the identity of A. perglabra. We have elected to conform to the works of Florin (1981), Haworth (1988), and Camburn and Kingston (1986) and refer to our material as A. perglabra. Both Florin (1981) and Camburn and Kingston (1986) discuss further the taxonomic history of A. perglabra.

Specimens in the A. perglabra complex were relatively rare and found only in a few Connecticut and Canadian Shield localities that were oligotrophic, slightly or highly acidic, and low in specific conductivity. Gronlund (1989) also reported A. perglabra primarily from acidic localities in Holocene diatomites from Finland. It is of interest to note that Camburn and Kingston (1986) found A. perglabra var. jloritziae to be the most widespread taxon of the genus in softwater lakes of the northern Great Lakes region.

Aulacoseira pseudoamericana (Camburn) comb.nov. Basiorzyrn: Melosira pseudoatnericc~na Camburn in

Camburn and Kingston (1986, Figs. 55-58 and 82); slide A.-G.C. No. 54238 at the Academy ofiNatural Sciences of Philadelphia.

Although we did not observe any specimens of this taxon in our collections we did examine type material from Cusino Lake (Michigan) and material from Dorothy Lake (Wisconsin) also supplied to us by Paul Hamilton (Figs. 66-7 1). Accord- ing to the original description the pervalvar axis is shorter than the diameter of the cell, the mantle is unornamented, and the periphery of the valve face is ornamented with two irregularly spaced rows of small areolae (Camburn and Kingston 1986).

Our observations confirm the main characteristics discussed by Camburn and Kingston (1986). First, except for a small groove where the spines from the adjacent cell were positioned (Figs. 66-68), the mantle was unornamented. Second, we generally observed two rings of small and irregularly arranged areolae positioned on the periphery of the valve face (Fig. 70). In addition, we noted that the spines were often flat in cross section, and many appeared to have squared distal tips (Figs. 66 and 68-70). Specimens had a very shallow Ringleiste (Figs. 69 and 71) and a rimoportula

near the junction of the valve face and mantle (Fig. 71). Based on our observations we believe this taxon is closely related to the A. perglabra complex.

Aulacoseira distans complex Taxa included in this complex have mantle height to valve diameter ratios that are usually equal to or less than one and have areolated valve faces. All of the taxa listed in this complex have been considered as varieties of A~ilacoseira distans (Ehrenberg) Simonsen, although some have been elevated to the species rank (Krammer 1991a; Krammer and Lange-Bertalot 1991). We include observations and (or) discussion of A. distatzs var. distans, A. distans var. nivaloides (Cambrun) comb.nov., A. distans var. nivalis (Wm. Smith) Haworth, Aulacoseira tenella (Nygaard) Simonsen, Aula- coseira hurnilis (Cleve-Euler) Simonsen, and Aulacoseira laevissima (Grunow) Krammer.

Aulacoseira distans (Ehrenberg) Simonsen Melosira distans Ehrenberg

Aulacoseira distans var. nivalis (Wm. Smith) Haworth Melosira distans var. nivalis Wm. Smith

Aulacoseira distans var. nivaloides (Camburn) comb.nov. Basionym: Melosira distans var. nivaloides Camburn

in Camburn and Kingston (1986, Figs. 18-23); slide A.-G.C. No. 5424 1 at the Academy of Natural Sciences of Philadelphia.

We encountered three populations that were difficult to distinguish between A. distans var. distans, var. nivalis, and var. nivaloides (Figs. 72-74, and 78-82). According to Haworth (1988) and Krammer (1991~) A. rlistatzs var. distatzs has a distinct and broad Ringleiste, often extending one third the diameter of the cell. A~ilacoseira distans var. nivalis (Haworth 1988; Krammer 1991a), and presumably A. distans var. nivaloides, lack a deep Ringleiste. Most authors (e.g., Camburn and Kingston 1986; Haworth 1988; Krammer 1991a) have stated that var. nivalis can also be distinguished from var. distans on the basis of its large and coarse valve- face areolae.

Our major difficulty was distinguishing A~ilacoseira distans var. tlivaloides from var. nivalis. According to Camburn and Kingston (1986) var. nivaloides differs from var. nivalis in having smaller areolae and lacking a ring of areolae on the peripheral-most part of the valve face. Haworth (1988, Fig. 66) depicted a cell of var. nivaloides that clearly had areolae on the periphery of the valve face and areolae that were equal or larger in size than the areolae on her var. nivalis specimens (her Figs. 6- 11). Camburn and Kingston (1986, p. 22) also stated that var. nivaloides "is characterized by the distinctive, dashlike punctae that comprise the striae and the convex or concave nature of the valve face;" however, they further stated that var. nivalis had "larger elongate punctae" than var. nivaloides (p. 22). On the basis of the comments made by Camburn and Kingston (1986) and their original light micrographs of var. nivaloides we found areolae shape to be a difficult feature to utilize. However, based on the figures depicted by Haworth (1988, compare Figs. 8 and 66) the mantle areolae are clearly more elongate

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Figs. 66-71. Observations made from Cusino Lake, Michigan, U.S.A. (Figs. 66-69 and 71; type niatcrial), and Dorothy Lake, Wisconsin (Fig. 70), of Aulucoseiru j~seu~loumericunu. Fig. 66. Two cells depicting the unornamented mantle region. Scale bar = 5 pm. Fig. 67. View of the junction of the valve face and mantle. Scale bar = I pm. Fig. 68. Cell depicting the unornamented mantle and nature of the spines. Scale bar = 1 pm. Fig. 69. Inside view depicting the nature of the areolae on the periphery of the valve face and the shallow Ringleiste. Scale bar = 1 pni. Fig. 70. Valve with two peripheral rings of circular areolae. Note the flat spines. Scale bar = I Km. Fig. 71. Close-up of Fig. 69 depicting the shallow Ringleiste, areolae, and the position of a rimoportula (arrow). Scale bar = 1 Km.

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Figs. 72-74. Aulctcoseira clistatls var. disrctns. Fig. 72. Vicw depicting both the valve face and mantle. Note the relatively straight. but oblique, rows of mantle areolae, the small valve-face areolae, and the large pores between each spine. Also note that there are two mantle costae per spine. Scale bar = 5 pni. Fig. 73. Valve view showing the areolae. Scale bar = 1 pm. Fig. 74. Vicw depicting the collum and the wide and thick Ringleiste. Scale bar = 2 pm. Figs. 75-77. A~l/c~co.seirc~ 1ctevi.ssitna. Fig. 75. Vicw depicting both the valve face and the niantle. Note the convex valve face, straight rows of small areolae on the mantle, and the sulcus. Scale bar = 2 pm. Fig. 76. Close-up of Fig. 77 showing details of the bases of the spines. Note that each spine spans approximately four to five mantle costae. Scale bar = 1 pm. Fig. 77. Mantle view depicting the small areolae in straight rows, the sulcus and collun~, and the long thin spines. Note the thin grooves where the spines from neighboring cells were positioned. Scale bar = 2 pnl.

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Figs. 78-82. Aulacoseira distarls var. nivaloides. Fig. 78. Close-up of Fig. 81 depicting the large circular areolae on the valve face and the more elongate mantle areolae. Note the anchor-shaped tips and small lateral projections on the spines. Scale bar = 1 pm. Fig. 79. Valve showing both the valve face and the mantle. Note the straight rows of elongate pores, the convex valve face and the relatively wide collum. Scale bar = 5 pm. Fig. 80. Close-up of Fig. 79. Note that a reticulation of ribs can be seen within each areolae. Also note the anchor-shaped tips on the spines. Scale bar = 1 pm. Fig. 81. Cell depicting a convex valve face and large areolae on both the valve face and the mantle. Scale bar = 5 pm. Fig. 82. Cell showing large relatively circular areolae on the valve face and elongate areolae on the mantle. Scale bar = 2 pm.

and dashlike on specimens of var. nivaloides than those of var. nivalis. We also noted, based on specimens pictured by Haworth (1988) and Krammer and Lange-Bertalot (199 l), that a spine terminates each mantle costae on var. nivalis, whereas the spines on var. tzivaloides were positioned approximately every two mantle costae.

Although specimens of these three varieties were rare in our study regions we had two populations that fit Krammer's (199la) description of A. distans var. distans (Figs. 72 -74), and two populations that we believe best fit the description of A. distans var. nivaloides (Figs. 78 - 82). Aulacoseiru distatzs var. distans valves ranged in diameter between 5 and 10 pm, had a mean mantle height of 5 pm, oblique mantle striae each with four to eight areolae, an areolate valve face, and a wide and thick Ringleiste (Figs. 72-74). Spines were relatively thick, formed by the coalescence of two mantle costae, and alternated with areolae that were larger in diameter than the remaining areolae on the valve face or mantle (Figs. 72-74). On the basis of the relatively small valve

areolae and the wide Ringleiste we believe these specimens are best described as A. distans var. distans.

Specimens that we believe are best identified as A. distans var. nivaloides had mostly convex valve faces with large and relatively widely spaced circular areolae and parallel rows of mantle striae consisting of elongate and dashlike areolae (Figs. 78-82). Cells most often had five or six areolae per mantle striae. A reticulum of ribs could be observed within all areolae. The overall size of specimens and the number of mantle striae and areolae per 10 pm fits the original description given by Camburn and Kingston (1986). Although not mentioned in the original description, our specimens possessed tapered spines, about 1 - 1.5 pm long, with small anchor-shaped tips and lateral siliceous knobs (Figs. 78 and 80). Spines were positioned every two or three mantle costae; we believe this feature may also help to separate var. nivaloides from var. nivalis.

Our specimens of A. distans var. rzivuloides matched nicely the one figured by Haworth (1988, Fig. 66) in areolae shape

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Figs. 83-86. Aulacoseira 1zutnilis. Fig. 83. View of the valve face depicting the relatively large areolae. Scale bar = 2 pm. Fig. 84. An intact frustule showing the long slender spines that terminate each mantle costae, parallel grooves on the mantle, and the wide collum. Scale bar = 2 pm. Fig. 85. Valve face view depicting the large areolae positioned in more or less tangential rows. Scale bar = 2 pm. Fig. 86. View of the mantle depicting the details of the parallel grooves. Note the large areolae that terminate each end of each groove and the long slender spines. Scale bar = 2 pm.

and distribution, spine and striae morphology, and the convex nature of the valve face. However, as discussed above, several characteristics did not fully conform with the original description. The areolae on the valve face of our specimens were relatively large, 0 .3 -0.5 pm in diameter, often irregular in shape, and covered the valve face. As such, the areolae were as large or larger than those of var. nivalis, and were not lacking on the peripheral region of the valve face as observed by Camburn and Kingston (1986). Although we found only two populations of var. tzivaloides in Connecticut, they were both from habitats low in specific conductivity, poorly buffered, low in nutrients, and slightly acidic.

Aulacoseira hurnilis (Cleve-Euler) Simonsen Melosira distans var. humilis Cleve-Euler Melosira distans var. blelhamensis Evans

Valves are characterized by an areolate valve face, long slender spines, and a very distinctive design on the mantle

(Figs. 83-86). The mantle consists of a series of parallel grooves each of which alternates with a ridge or costa. A spine terminates each mantle costae. Both ends of each mantle groove are terminated by a large areolae (Figs. 84 and 86); the areolae form two distinct transverse rows that are easily discernible with LM, especially the row along the collum (Florin 1981). In our specimens, additional finer or delicate areolae were not always observed in the grooves between the large terminal areolae as reported by Evans (1964). Although the long slender spines were often broken, the tips of intact specimens appeared to be slightly swollen.

The areolae on the valve face were relatively large and most often positioned in concentric rows (Figs. 83 and 85). The areolae along the periphery of the valve face were generally larger than those in the center. Most specimens had convex valve faces (e.g., Fig. 86), although several with more or less flat valve faces were also observed. The collum was smooth and often accounted for at least one third the

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mantle height (Fig. 86). The Ringleiste and rimoportulae were not studied, and a sulcus was not apparent.

Florin (198 1) provided an excellent account of the history of this taxon and its synonymy with Melosira distans var. blelharnensis. Aulacoseria humilis was very rare, observed in only three Connecticut lakes low in specific conductivity and with a pH between 5 and 6 , in several lakes on the Canadian Shield, and in a few arctic lakes with low specific conductivity and a pH between 7 and 8.

Aulacoseira laevissima (Grunow) Krammer A. distans var. laevissima (Grunow) Haworth Melosira distans var. laevissima Grunow

We found a few specimens that we believe are best described as A. laevissirna (Figs. 75-77). According to Haworth (1988), valves of this taxon have a diameter approximately equal to the mantle height, a "typical distatzs pore pattern" on the valve face, and numerous, 21 -28 in 10 pm, straight rows of mantle areolae. In addition, Haworth (1988) observed that the areolae were small, and the spines were long, pointed and with "anchor-shaped tips."

The diameter of our specimens (ca. 8 - 11 pm), density and orientation of mantle striae (ca. 22-24 per 10 pm), number of areolae per 10 pm within a striae (24 to 28), and the fine structure of areolae are similar to those observed by Haworth (1988). In addition, our specimens had areolate valve faces that were usually convex in shape, straight pervalvar striae composed of very small areolae, a relatively wide collum, a distinct sulcus, and long slender spines with slightly swollen tips and small lateral bumps (Figs. 75-77).

Our specimens appeared to differ from those pictured by Haworth (1988, Figs. 12- 15) in the number of mantle costae per spine. Specimens depicted by Haworth had a spine every two or three mantle costae. The bases of the spines of our specimens were very broad and often spanned four or five mantle costae (Figs. 76 and 77). In addition, we observed thin grooves on the mantle where the spines from neighboring cells were positioned (Figs. 76 and 77). With two minor exceptions, our specimens also closely matched those described by Krammer and Lange-Bertalot (1991); these authors stated that this taxon had a flat valve face and diag- onally positioned mantle striae. Although we did not observe the nature of the Ringleiste, Krammer and Lange-Bertalot (1991) stated that it extended about one third the diameter of the valve, while Haworth (1988) reported that it (the pseudoseptum) was very shallow. The taxon was only observed in two Connecticut waterbodies low in specific conductivity

Aulacoseira tenella (Nygaard) Simonsen Melosira tenella Nygaard Melosira distans var. tenella (Nygaard) Florin

Valves are characterized by a very small mantle height to valve diameter ratio, often close to 0.2 (Figs. 87-92). The range in the diameter of valves in our collections was very small, between 5 and 7 pm, in close agreement with reports by Nygaard (1956) and Camburn and Kingston (1986), but on the lower end of the range given by Krammer and Lange- Bertalot (1991). The mean height of the mantle was 2 pm, although some specimens had a mantle height close to only 1 pm (Fig. 90). The valve face is covered with evenly spaced areolae each of which is covered with a velum on the inside

of the valve (Fig. 9 I), as was pointed out by Nygaard (1956). The velum often becomes eroded (Fig. 92). The areolae on the periphery of the valve face are often slightly wider in diameter and positioned in concentric rings (Figs. 88 and 89). The valve face is most often flat and sharply delineated from the mantle by a ridge (Figs. 87-90). The ridge appears to be formed, in part, from the bases of short teethlike spines (Fig. 89). In our samples the spines .were often worn or eroded, and filaments of more than two cells were not observed. Florin (1981, Figs. 1 1 - 12 of Plate 2) also pictured valves with relatively short pointed spines.

There are two or three areolae per pervalvar row on the mantle (Figs. 87-92), and all areolae are of approximately the same diameter. It is not uncommon for an areolae to be missing from a pervalvar row (Fig. 90), a feature also depicted by Florin (198 1, Fig. 4). Each mantle costa terminates in a spine and is often ornamented with siliceous knobs or thickened regions (Figs. 89 and 90). We observed one or two rimoportulae positioned near the collum at the end of a row of areolae (Figs. 91 and 92). The mean height of the collum on our specimens was 0.5 pm, and the Ringleiste was very shallow or absent (Figs. 91 and 92); this latter characteristic differs from the definition of taxa within the A. distans complex given by Krammer and Lange-Bertalot (1991), who commented that A. tenella needed further research.

Aulacoseira tenella has been defined as an acidophilous taxon (Nygaard 1956; Florin 1981; Camburn and Kingston 1986), often found between pH 4 and 6. In Connecticut, this taxon was most common in localities with a pH between 5 and 7, low in alkalinity, and oligotrophic to early mesotrophic in nature. The organism was not found in the few lakes with a pH < 5 and was lacking from all prairie localities in Canada.

Aulacoseira lirata and Aulacoseira alpigena

Aulacoseira lirata (Ehrenberg) Ross in Hartley Melosira lirata (Ehrenberg) Kiitzing

Aulacoseira alpigena (Grunow) Krammer Aulacoseira distans var. alpigena (Grunow) Simonsen Alilacoseira lirata var. alpigena (Grunow) Haworth Melosira distans var. alpigena Grunow

Based on current literature descriptions we had difficulty making distinctions between A. lirata and A. alpigena, primarily because of the overlap in characteristics and because we always found both taxa tbgether. Thus, we have elected to discuss both taxa together.

According to Haworth (1988) Aulacoseira lirata generally has five-or six areolae per striae, which are somewhat coarse in nature and aligned in straight rows. Aulacoseira alpigena has a wider range in the number of areolae per striae, from 4 to 15 (Haworth 1988; Krammer and Lange- Bertalot 1991), that are often finer in nature and positioned in curved rows (Haworth 1988; Krammer 1991~) . Our specimens had a fairly wide range in the number of areolae in a pervalvar striae, from 5 ti 12, and the pervalvar rows of areolae were either straight, oblique, or curved (Figs. 93- 99). Based on these features specimens in Figs. 95 and 98 would best fit A. lirata, while those in Figs. 93, 94, 96, 97, and 99, A. alpigena. However, we often found specimens with greater than six areolae per striae that were straight and

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Figs. 87-92. Aulacoseira [enella. Fig. 87. Two sibling cells. Notc the short mantle height to valve diameter ratio and the sharp delineation of the valve face from the mantle. There are mostly two areolae per pervalvar row on the mantle. Scale bar = 2 pm. Fig. 88. Whole frustule depicting both the valve face and the mantle. Notc the ridge that separates the valve face from the mantle. Scale bar = 5 pm. Fig. 89. Valve depicting the areolae on the valve face and mantle. Note the knobs of silica between the areolae on the valve face. Scale bar = 5 pm. Fig. 90. Girdle view of a valve with a mantle depth of ca. 1.5 pm. Note the pervalvar row with a single areola. Scale bar = 2 pm. Fig. 91. Inside view of a valve depicting the location of a rimoportula (arrow). Also note that each areola is covered by a velum. Scale bar = 2 pm. Fig. 92. Inside view of a valve depicting the location of two rimoportulae (arrows) and a shallow Ringleiste. Scale bar = 2 pm.

not curved. We also found several filaments with cells that Krammer ( 1 9 9 1 ~ ) described A. alpigena as having linking had both straight and slightly curved pervalvar rows of areolae spines that were spatulate in shape with lateral projections, (Fig. 93). whereas A. lirata has been noted to have cruciform-shaped

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1830 Can. J. Bot. Vol. 75. 1997

Figs. 93-99. Figs. 93, 94, 96, 97, and 99 are of Artlacoseira cllpigetlcl. Figs. 95 and 98 are of A~ilacoseira lirarcr. See text for details. Fig. 93. Filament depicting valves with straight and curved rows of pervalvar areolae. Scale bar = 10 p n ~ . Fig. 94. Filament with valves possessing relatively straight rows of pervalvar areolae. Scale bar = 5 pm. Fig. 95. Cell depicting the structure of the Ringleiste. Scale bar = 5 pm. Fig. 96. Valve depicting curved pervalvar rows of areolae, a smooth valve face and spines terminating every mantle costae. Scale bar = 2 pm. Fig. 97. Close-up of a valve showing the irregular fingerlike projections on the spines. Scale bar = 1 p n ~ . Fig. 98. Close-up depicting the linking spines and mantle areolae. Note the cruciform shape of the spines. Scale bar = 2 pm. Fig. 99. Close-up of a cell depicting linking spines. Most spines are irregular in shape owing to the lateral projections. Note the cruciform-shaped spine (arrow). Scale bar = I pm.

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Siver and Kling

linking spines (Haworth 1988). Using this feature specimens in Figs. 93, 94, 96, 97, and 99 are best described as A. alpigena, and those in Figs. 95 and 98 as A. lirata; these distinctions fit those made based on mantle striae features. However, it was not difficult to find cells with essentially both types of spines (Fig. 99).

Because both A. lirata and A. alpigena have smooth, plain valve faces with usually a single peripheral ring of areolae, this character could not be used to separate the taxa. Most of our specimens had a single peripheral ring of areolae on the valve face. According to the literature the structure of the Ringleiste (pseudoseptum in the sense of Haworth 1988) differs in the two taxa. Florin (1981) and Haworth (1988) stated that A. lirata possessed a deep and obvious Ringleiste, whereas the Ringleiste of A. alpigena was shallow and small (Krammer 1991a). Also, as pointed out by Krammer (1991a), although Haworth (1988) listed A. alpigena as having a "deep pseudoseptum" her figures depict a shallow one. We had a difficult time using this character because the Ring- leiste was almost always what we would consider as deep and obvious (e.g., Fig. 95); based on this single character, most, if not all, of our specimens would be best described as A. lirata.

Our specimens that keyed to A. lirata according to mantle areolae, striae characters, and spine morphology were always slightly wider than long and fit the dimensions given by Haworth (1988). However, specimens that keyed to A. alpigena based on areolae, striae, and spine features were always longer than wide and did not fit the height dimensions listed in Haworth (1988).

We conclude that both taxa should remain separate at this time but that further work needs to be done to determine if indeed they are separate species. It could be that these two taxa represent the ends of a continuum. At one end are specimens similar to A. lirata, with a small mantle height to valve diameter ratio, few areolae per striae that are arranged in parallel rows, and a large Ringleiste. At the other end of the continuum are specimens similar to A. alpigena, with larger mantle height to valve diameter ratios, more areolae per mantle striae arranged in rows often spiralled or curved, and possessing a smaller Ringleiste. The morphology of the valve face and spines remains similar for specimens at both ends of the continuum.

Both taxa were only found in Connecticut and Canadian Shield localities with a pH between 5 and 6 and low in specific conductivity and nutrient concentrations. Gronlund (1989) also reported both taxa, along with A. lacustris, as dominant acidophilous taxa in Holocene diatomites from Finland.

Aulacoseira lacustris (Grunow) Krammer Melosira lyrata var. lacustris Grunow in Van Heurck

The primary distinguishing feature of this taxon is the structure of the mantle areolae (Figs. 100- 105). Areolae range in shape from circular to elongate, are aligned in rows that are parallel to the pervalvar axis, and appear to be situated in two tiers or layers. The areolae of the inner layer are usually (but not often) circular in nature and situated in rows between the costae (Fig. 100, right arrow). It appears that once this inner layer of areolae is made the organism adds another layer of silica to the costae regions forming flat ridges (Figs. 100 and 104). The silica of this secondary layer

also becomes deposited around and sometimes on the inner rows of areolae, forming an outer layer also with rows of areolae (Fig. 100, left arrow). The silica of the secondary layer is usually more regularly deposited closest to the collum and more irregularly deposited towards the valve face; this results in more elongate openings near the valve face. Some- times the secondary layer fills in completely resulting in areas of the secondary layer missing areolae. Areolae of the inner and outer layers are not always aligned with each other.

It is possible that the irregularly deposited silica of the secondary layer is the result of an incomplete deposition process. If this is the case, it seems reasonable that the deposition of the secondary layer begins near the collum (and is thus more complete) and ends near the valve face. We have observed one specimen where it appears that the secondary layer was deposited only on the lower half of the valve. It is unclear to us whether a cell lacking a secondary layer would still be identified as A. lacustris. With this in mind and since we have only observed populations of A. lacustris in localities with A. lirata and A. alpigena, we believe this raises the question of the true relationship between A. lacustris and these latter two species.

The valve face of our specimens was smooth, relatively flat, lacked areolae (Figs. 102 and 103), and was similar in structure to those depicted by Florin (1981, Fig. 26) and Haworth (1988, Fig. 64). Although Krammer (199 1b) noted there could be specimens with "incomplete areolae on the whole discus" (see his Figs. 47 and 48), we did not observe valves with such a morphology. Linking spines arose from a single pervalvar costae (Krammer 1991b), were highly irregular in shape, and appeared to be more or less molded around neighboring spines (Figs. 100- 104). The Ringleiste extended only a short distance into the cell (Fig. 105), and the collum was often quite tall (Figs. 102 and 103).

Aulacoseira crassipunctata Krammer Dimensions of valves and the mantle height to valve diameter

u

ratio of this species matched those given in the original description by Krammer (1991b). Mantle areolae are very large, mostly circular in outline, widely spaced, and arranged in mostly straight rows (Figs. 106- 11 1). In general, because of the irregular spacing of areolae in each pervalvar row, the areolae do not become aligned in transverse rows.

Krammer (1991b) observed a variety of designs on the valve face, ranging from those with few irregularly dis- tributed areolae to ones covered with areolae, sometimes in concentric rows. Most of our specimens had valve faces with a layer of irregularly deposited silica and a few scattered areolae (Figs. 106 and 107); we did not observe cells with completely areolate valve faces. Valve faces were often concave or convex.

As noted by Krammer (1991b) we observed only linking spines (Figs. 108 and 109). Spines were irregular, highly lobed in design, and essentially molded to the shape of the grooves in which they were situated (Fig. 108). The collum was rather tall and ornamented with parallel pervalvar rows of small papillae (Figs. 110 and 1 11). Although we cannot comment on the Ringleiste, Krammer (1991b) noted that it was very thick in nature. Rimoportulae were not observed.

Specimens of this rather rare taxon were observed in three acidic Connecticut localities low in specific conductivity.

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Figs. 100-105. A~llacoseirci l l c~nfr i s . Fig. 100. Close-up depicting the highly irregularly shaped linking spines and details of the mantle costae and areolae. Note the inner (right arrow) and outer (left arrow) mantle areolae. See text for details. Scale bar = 2 pm. Fig. 101. Filament depicting valves with straight rows of pervalvar areolae. Note that some areolae are small and circular while others are larger and elongate. Scale bar = 5 pm. Fig. 102. Close-up of the filament in Fig. 103. Valve depicting the smooth nature of the valve face, the collum, and the irregular-shaped mantle areolae. Scale bar = 2 pni. Fig. 103. Filanicnt depicting girdle bands. Scale bar = 5 pm. Fig. 104. Close-up of two valves showing the nature of the linking spines and the secondary layer of silica deposited on the mantle. See text for details. Scale bar = 2 pm. Fig. 105. Specimen depicting the shallow Ringleiste. Scale bar = 5 pm.

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Figs. 106-111. Altlacoseirn crnssipunctatn. Fig. 106. Cell depicting the nature of the mantle and girdle bands. Note that mantle areolae are in straight rows. Scale bar = 5 pm. Fig. 107. Valve showing the valve face and large and widely spaced mantle areolae. Scale bar = 2 pm. Fig. 108. Close-up of two valves showing details of the highly irregular linking spines. Scale bar = 2 ym. Fig. 109. Close-up of the linking spines and mantle areolae. Note the widely spaced areolae. Scale bar = 2 pm. Fig. 110. Close-up of Fig. 106. Note the wide collum with rows of small siliceous knobs. A step on the mantle is evident. Scale bar = 2 pm. Fig. I1 I. Valve with a wide collum possessing rows of small siliceous knobs. Scale bar = 2 pm.

Aulacoseira crassipunctata is quite distinct from other species Conclusions in the genus, except for Aulacoseira canadensis (Hustedt) Simonsen. As pointed out by Krammer (1991b) the latter (1) Many morphological details of the frustules of Aula- taxon has even larger mantle areolae and differently shaped coseir-a species can best be critically examined with linking spines. the SEM, As a result, we believe the SEM should be

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routinely incorporated into studies where the taxonomic identity of many species of Aulacoseira is critical.

(2) Several species of Aulacosiera are polymorphic with respect to some of the characteristicsr~utinel~ utilized to distinguish species. For example, as the mantle height to valve diameter ratio increased on specimens of A. subarctica, the size and degree to which the Ring- leiste extended into the cell decreased. In a similar manner, pervalvar rows of areolae also became more spiralled or curved as the mantle height to valve diameter ratio of A. subarctica valves increased. It is also obvious that, in taxa such as A. subarctica with a wide range in the mantle height to valve diameter ratio, there will be a correspondingly wide range in the number of areolae in a pervalvar row. Filaments of A. granulata also possessed valves with straight pervalvar rows of areolae as well as ones that were distinctly spiralled. Aulacoseira islandica often formed filaments that were polymorphic in regards to the shape and distribution of areolae when found growing in open water but more or less isomorphic in nature when found under the ice. These observations suggest to us that, at least in some species, the alignment of pervalvar rows of areolae, the number of areolae per row, and perhaps the size of the Ringleiste should be used with caution in delimiting species. In this regard, it would be of value to determine if the size of the Ringleiste in taxa where it is a critical taxonomic feature, e.g., A. lirata and A. alpigena, is polymorphic or constant in nature.

(3) The position of the rimoportulae appeared to be a constant trait in many species and should be further considered as an important and useful taxonomic character in the genus Aulacoseira.

(4) Specimens with curved mantle striae were always spiralled in a right-handed manner (see text for details). Although we do not know the significance of this feature, it would be of interest to determine if all specimens of Azrlacoseira in other regions of the world share this trait.

(5) Aulacoseira perglabra var. perglabra (sensu Florin 1981 and Haworth 1988) appears to be a well-defined taxon, although according to Krammer (1991a), there is some confusion regarding its name. We found such a high degree of variation in the morphology of the mantle on specimens of A. perglabra var.>erglabra that it was difficult to use this character to distinguish it from A. perglabra var. Joriniae. We did not, however, observe populations with a valve-face morphology typical of that described by Camburn and Kingston (1986) for A. perglabra var. Joriniae. We conclude, as did Haworth (1988), that further taxonomic work needs to be done on these taxa.

(6) We found the number of areolae per mantle striae and the orientation of the areolae to be difficult characters to separate A. lirata from A. alpigena. We also found a few specimens with linking spines characteristic of both taxa on the same valve. Based on the characteristics of the Ringleiste all of our specimens would key to A. lirata. We suggest that these taxa are very closely related and may indeed represent the ends of a continuum.

(7) We conclude that further observations are needed to determine the nature. of the deposition of silica in

A. lacustris. Our observations have made us consider the possibility that if the outer layer of silica was not deposited on specimens of A. lacustris, they may in fact resemble other species (e.g., A. alpigena).

(8) We used the presence of a wide Ringleiste and the nature of the valve areolae as primary characters to separate A. distans var. distans from A, distans var. nivalis and A. distans var. nivaloides. In light of the polymorphic nature of the Ringleiste in some species, we believe that further observations on the stability of the Ringleiste in A. distans var. distans would be of value. Our main difficulty was in distinguishing A. distans var. nivaloides from A. distans var. nivalis. In addition to the characteristics already used to separate these varieties, we suggest that the ratio of spines to mantle costae could also be a useful feature.

(9) All taxa discussed in this paper, except for A. islandica and A, crenulata, were found in Connecticut. Aula- coseira ambigua, and to a lesser degree A. subarctica and A. tenella, were clearly the most common species in Connecticut localities. A group of taxa, including A. lirata, A. alpigena, A. perglabra, and A. lac~rstris were primarily restricted to acidic habitats low in specific conductivity. Another group of taxa, including varieties of A. distans, A. crassipunctata, A. laevissima, A. hlrmilis, and A. italica were rare and, based on preliminary observations, more common in older sediment remains. To our surprise A. granulata was quite rare in Connecticut habitats and restricted to the more eutrophic lakes.

(10) Aulacoseira subarctica, A. ambigua, A. islandica, and A. hurnilis were the most common species in both large and small boreal lakes in Canada. A~ilacoseira tenella dominated in small Canadian Shield lakes that were slightly acidic or neutral in nature. As lakes on the shield became more acidic (pH below 5.5) A. lirata, A. alpigena, A. lacustris, and taxa in the A. perglabra complex became more abundant. Aulacoseira ambigua, A. grarz~rlata, and A. islandica were the most common species in large prairie lakes such as Lake Winnipeg and Lake Manitoba.

Acknowledgements

This project was funded, in part, with grants from the National Science Foundation (no. DEB-9306587) and The Conservation and Research Foundation.

References

Battarbee, R.W. 1984. Diatom analysis and the acidification of lakes. Philos. Trans. R. Soc. London B, 305: 451 -457.

Battarbee, R.W. 1986. Diatom analysis. 111 Handbook of Holocene palaeoecology and palaeohydrology. Edited by B.E. Berglund. John Wiley & Sons, New York. pp. 527-570.

Birks, H.J.B., Line, J.M., Juggins, S., Stevenson, A.C., and ter Braak, C. J.F. 1990. Diatoms and pH reconstruction. Philos. Trans. R. Soc. London B, 327: 263 -277.

Camburn, K.E., and Kingston, J.C. 1986. The genus Melosira from soft-water lakes with special reference to northern Michigan, Wisconsin and Minnesota. In Diatoms and lake acidity. Edited by J.P. Smol, R.W. Batterbee, R.B. Davis, and

O 1997 NRC Canada

Can

. J. B

ot. D

ownl

oade

d fr

om w

ww

.nrc

rese

arch

pres

s.co

m b

y N

C S

TA

TE

UN

IVE

RSI

TY

on

10/1

1/12

For

pers

onal

use

onl

y.

Siver and Kling

J. Merilainen. pp. 17-34. Dr. W. Junk, Dordrecht, the Nether- lands.

Canavan, R.W., IV, and Siver, P.A. 1994. Chemical and physical properties of Connecticut lakes with emphasis on regional geology. Lake Reservoir Manage. 10: 175 - 188.

Charles, D.F. 1985. Relationships between surface sediment diatom assemblages and lakewater characteristics in Adirondack lakes. Ecology, 66: 994 - 10 1 1.

Cumming, B.F., Smol, J.P., Kingston, J.C., Charles, D.F., Birks, H.J.B., Camburn, K.E., Dixit, S.S., Uutala, A.J., and Selle, A.R. 1992. How much acidification has occurred in Adirondack region lakes (New York, USA) since preindustrial times? Can. J. Fish. Aquat. Sci. 49: 128- 141.

Edlund, M.B., Stoermer, E.F., and Taylor, C.M. 1996. A~ilaco.sei,n skvortzo~vii sp.nov. (Bacillariophyta), a poorly understood diatom from Lake Baikal, Russia. J. Phycol. 32: 165 - 175.

Evans, G. 1964. Two fossil diatoms from the lake deposits of the English Lake District. New Phytol. 63: 413-417.

Florin, M.-B. 1981. The taxonomy of some Melosirn species, a comparative morphological study 11. Iti Proceedings of the 6th Symposium on Recent and Fossil Diatoms, Budapest, Hungary. 1980. Edited by R. Ross. Koeltz. Koenigstein, Germany. pp. 43 -73.

Genkal, S.I., and Popovskaya, (3.1. New data on the frustule morphology of A~il~rco.sirr~ i.slntdica (Bacillariophyta). Diatom Res. 6: 255-266.

Genkal, S.I., Balonov, I.M., and Korneva, L.G. 1986. Morphology and taxonomy of Melosirn islr~tlclicn O.F. Muller (Bacillario- phyta). Biology of Inland Waters Inf. Bull. No. 72. pp. 14-21.

Gronlund, T. 1989. Holocene diatomites in central Finland, with special reference to Aulacoseitn (Melosira) species. Rep. No. 87. Geological Survey of Finland. Helsinki, Finland.

Hall, R.I., and Smol, J.P. 1992. A weighted-averaging regression and calibration model for inferring total phosphorus concentration from diatoms in British Columbia (Canada) lakes. Freshwater Biol. 27: 417-434.

Haworth, E. 1988. Distribution of diatom taxa of the old genus Melosirn (now mainly Aulc~cosei,ur) in Cumbrian waters. Itr Algae and aquatic environment. Eclite~lt~y F.E. Round. Biopress, Ltd.. Bristol, England. pp. 138 - 168.

Jewson, D.H. 1992. Size reduction, reproductive strategy and the life cycle of a centric diatom. Philos. Trans. R. Soc. London B, 336: 191-213.

Jewson, D.H.. Khondker, M., Rahman. M.H., and Lowry, S. 1993. Auxosporulation of the freshwater diatom Airlc~cosei,n lrerzogii in Lake Banani. Bangladesh. Diatom Res. 8: 403-418.

Kobayasi, H., and Nozawa, M. 1981. Fine structure of the fresh water centric diatom A~ilacoseirn att10igua (Grunow) Sim. Jpn. J. Phycol. 29: 121 - 128.

Kobayasi, H., and Nozawa, M. 1982. Fine structure of the fresh water centric diatom Airlncoseirc~ itnlicn. Jpn. J. Phycol. 30: 139- 146.

Kozhova, O.M., Shastina, N.A., and Kaplina, G.S. 1982. Size

characteristics of Melosira islntldica subsp. lielvetim 0 . Mull. from Lake Baikal. Hydrobiol. J. 18: 6-10.

Krammer, K. 19910. Morphology and taxonomy in some taxa of the genus A~ilncoseirn Thwaites (Bacillariophyceae). I. Aula- coseirn rli.stans and similar taxa. Nova Hedwigia. 52: 89- 112.

Krammer, K. 19910. Morphology and taxonomy in some taxa of the genus Aulncoseir~z Thwaites (Bacillariophyceae). 11. Taxa in the A. ~ ~ c I ~ I L I I ~ ~ L I - , itnlica- and lirnta- groups. Nova Hedwigia, 53: 477-496.

Krammer, K., and Lange-Bertalot. H. 1991. Bacillariophyceae, Teil 3: Centrales, Fragilariaceae, Eunotiaceae. Susswasserflora Mitteleuropa (founded by A. Pascher) 213. pp. 1-576. Fischer, Stuttgart, Germany.

Le Cohu, R. 1991. Morphologie des valve et de cingulurn chez A~ilncoseira atnbigl~i (Grun.) Simonsen (Bacillariophyceae): quclques observations sur les phases pre et post auxospores. Nova Hedwigia, 53: 409-421.

Le Cohu, R. 1996. Further observations and some comments on the fine structure of the centric diatom A~ilnco.seirn i.slntlrlicr~ (Bacillariophyceae). J. Phycol. 32: 333-338.

Likhoshway, Y .V., Yakushin, A.O., Puzyr, A.P., and Bondarenko, N.A. 1992. Fine structure of the velum and girdle bands in A~ilncoseira bnicnlensis. Diatom Res. 7: 87-94.

Nygaard, G. 1956. Ancient and recent flora of diatoms and Chrysophyceae in Lake Gribso. Folia Limnol. Scand. No. 8. pp. 32-262.

Renberg, I. 1976. Palaeolimnological investigations in Lake Prastjon. Early Norrland, 9: 1 13 - 159.

Ross, R., Cox, E.J., Karayeva, N.I., Mann, D.G., Paddock, T.B.B., Simonsen, R., and Sims, P.A. 1979. An amended terminology for the siliceous components of the diatom cell. Beih. Nova Hedwigia No. 64. pp. 513-533.

Round, F.E., Crawford, R.M., and Mann, D.G. 1990. The diatoms: biology and morphology of the genera. Cambridge University Press, New York.

Simonsen, R. 1979. The diatom system: ideas on phylogeny. Bacillaria, 2: 9-71.

Siver, P.A. 1987. The distribution and variation of S ~ I I L I ~ L I species (Chrysophyceae) in Connecticut, USA. Nord. J. Bot. 7: 107- 116.

Stoermer, E.F., Kreis, R.G., and Sicko-Goad, L.A. 1981. A systematic, quantitative and ecological comparison of Melosira islatrrlicc~ 0 . Mull. with M. grr~tlrrlarn (Ehrenberg) Ralfs from the Laurentian Great Lakes. J. Great Lakes Res. 7: 345-356.

Stoermer, E.F.. Wolin, J.A., Schelske, C.L., and Conley, D.J. 1985. Variations in Melosi,n islatrclica valve morphology in Lake Ontario sediments related to eutrophication and silica depletion. Lirnnol. Oceanogr. 30: 4 14-4 18.

Swift, D.M., and Wheeler, A.P. 1992. Evidence of an organic matrix from diatom biosilica. J. Phycol. 28: 202-209.

Thwaites, G.H.K. 1848. Further observations on the Diatornaceac with descriptions of new genera and species. Ann. Mag. Nat. Hist. Scr. 2. No. 1. pp. 161-172.

O 1997 NRC Canada

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Morphological observations of Aulacoseira using scanning electron microscopy

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