This article was downloaded by: [University of Guelph]On: 27 August 2012, At: 01:04Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Diatom ResearchPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tdia20

THE FRUSTULE STRUCTURE OF ORIGINALMATERIAL OF AULACOSEIRA DISTANS(EHRENBERG) SIMONSENRichard M Crawford a & Yelena Likhoshway ba Alfred Wegener Institute for Polar and Marine Research, Postfach,120161, 27575, Bremerhaven, Germanyb Limnological Institute, P.O. Box 4199, 664033, Irkutsk, Russia

Version of record first published: 31 Oct 2011

To cite this article: Richard M Crawford & Yelena Likhoshway (1999): THE FRUSTULE STRUCTUREOF ORIGINAL MATERIAL OF AULACOSEIRA DISTANS (EHRENBERG) SIMONSEN, Diatom Research, 14:2,239-250

To link to this article: http://dx.doi.org/10.1080/0269249X.1999.9705468

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.

Diatom Research (1999) Volume 14 (2), 239-250

THE FRUSTULE STRUCTURE OF ORIGINAL MATERIAL OF AULACOSEIRA DISTANS (EHRENBERG) SIMONSEN

Richard M Crawford

Alfred Wegener Institute for Polar and Marine Research, Postfach 120161, 27575 Bremerhaven, Germany

Yelena Likhoshway

Limnological Institute, P.O. Box 41 99, 664033 Irkutsk, Russia

The original material from which Ehrenberg described Gullionellu distuns has been examined with light and electron microscopy with a view to understanding the morphology of a taxon that is now within the genus Aulucoseira and has a number of varieties.

Aulucoseira distans has a distinctive heterovalvy, the “separation valves” that have no spines; areolae over the whole of the valve face; spines on the mantle edge are usually positioned between rows of areolae on the mantle which are in more or less straight rows; and a deep, thick ringleist with numerous rimoportulae against its inner side. Cells are found in short chains. This combination of characters does not match that in most published illustrations of A. &stuns and brings into question the taxonomic relationships of some of the published varieties. A lectotype has been chosen and deposted at BHU (the Ehrenberg collection at the Museum fur Naturkunde der Humboldt-Universitat in Berlin, and an isolectotype at BRM, (Bremerhaven).

INTRODUCTION

Of the species that are today included in the important freshwater planktonic genus Aulucoseira, the first to be named and illustrated, by Ehrenberg, was Gallionella distuns. Ehrenberg first used the name in 1836 although in 1848 Thwaites chose G. crenulata Ehrenberg as the type species when he erected the genus Aulacoseira. It was not until 1979 that the combination Aulacosira distans was made by Simonsen. Since 1836 a number of varieties and forms of the species have been described, all of them being very small specimens in which the characters are difficult to discern with the light microscope. Unfortunately, the precise characters of A. distans (Ehrenberg) Simonsen have not yet been fully established using the electron microscope. This may be due to the fact that it appears to be scarce in recent assemblages although it was present in great quantities in the material from which Ehrenberg first illustrated it. Recently, we had an opportunity to examine some of the original material from Bilin that Ehrenberg obtained through Klaproth. Not only is there plenty of material but the dried deposit is extremely rich in frustules in remarkably good condition. Indeed, so good is the material that we have been able to add information to that already presented from the light microscopy of this material by Krammer (1991a). Ultimately, we hope to use this information to assess the taxonomic relationships of the various forms and varieties of A. distans.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

240 R. M. CRAWFORD AND Y. LIKHOSHWAY

MATERIAL AND METHODS

All of the material illustrated in this paper was kindly made available from the Ehrenberg diatom collection at the Museum fur Naturkunde, Berlin by Dr David Lazarus. A comprehensive account of the collection itself has recently been published by Lazarus and Jahn (1998). For light and electron microscopy dried specimens from Bilin, packet F (labelled: “Bilin, reiner Poliershief.”) was used and prepared according to standard methods for examination with a Zeiss Axioplan light microscope and an IS1 DS130 scanning electron microscope.

OBSERVATIONS

Light microscopy

Fortunately, in the Bilin material there is evidence of a recent sexual phase as some initial valves can be found (Figs 1, 2, 2a) Consequently, and allowing for the possibility that larger auxospores may be formed, something near the maximum for the size range of the species can be observed and measured and the range of form appreciated (Fig. 2, 2a). The breadth of the immediate post auxospore valves is much greater than the height of the mantle; later in the size reduction process the valves are square in girdle view and even smaller valves are somewhat longer than wide. This tendency is common among species of Aulucoseiru and has recently been documented for A. ceretunu Haworth & Sabater (1993). A. distuns is one of the smaller species in this genus; Kutzing (1865, p. 54) gives a valve width up to 18 pm whilst quoting Ehrenberg’s published range of 4-35 pm. However, we could only find “GuiZZoneZZu distuns ... 1/288 einer (Paris) Linie grot3 (i.e. 8 pm), vie1 sind kleiner, weniger etwas grol3er” (Ehrenberg 1836). The smallest valves we measured were 4 pm, but the largest auxospore initial valve was found to be only 16 pm. As this is theoretically near the maximum breadth it is surprising that the value is only half of the upper limit allegedly given by Ehrenberg. That value must be doubted. The length of the widest valves we measured was 8-10 pm and that of the smallest valves, 10 pm, meaning that even though the cells become narrower with each cell division they do not also become correspondingly shorter. There is a short collar and the areolae on the valve mantle are usually arranged in more or less straight rows. Occasionally the rows of areolae are oblique to the pervalvar axis and, as in most other species except A. itulicu (Ehrenberg) Simonsen, appear to curve to the right (dextrorse, Fig. 8, arrow). The valve face is covered with randomly distributed areolae and no valves have been found in this material without a full covering of the valve face (Figs 3,4, 5). Also in valve view but in a different focus, the deep ringleist can be seen (Figs 2 & 7). This feature is also visible in mid-focus although it is not very clear unless seen in a fragment because of the thickness of the valve relative to its size (Fig. 9, arrow). The ringleist and the overall form of the valves/cells are, in fact, the most obvious features illustrated by Ehrenberg (Fig. 1). In valve view, if the focus is changed very slightly from the ringleist itself, the numerous rimoportulae are visible (Figs 2, 7, 8). As few as six and as many as 12 to 13 rimoportulae were found on small and large valves respectively. Spines can be seen on the margin of many valves but in most cases at least some of the spines are broken. The spines occur regularly between the last areola in a row on the mantle (Fig. 6).

Electron microscopy

The size range and quality of the preservation of this material can be best appreciated using the scanning electron microscope (Figs 3, 10-21). The diatom can be found in short chains of 2 or 3 cells and, surprisingly for fossil material, the girdle bands are still intact in many cases (Figs 10, 12, 15).

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

AUUCOSEIRA DISTANS 241

All material illustrated is from Bilin, Box C. Fig. 1. A drawing of several frustules made by Ehrenberg from the Bilin material. Zeichenblatt 2421.

The pores in the girdle bands are very fine and typical of those found in other Aulucoseiru species (Crawford 1980, Kobayashi & Nozawa 1982, Likhoshway et al. 1992).

The short, pointed spines are distinctive in that their bases are so neatly circumscribed that they give the impression of having been stuck onto the surface of the mantle/valve face rim (Fig. 11). This

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

242 R. M. CRAWFORD AND Y . LIKHOSHWAY

contrasts with many other species, of which A. suburcticu (0. Muller) Haworth is an extreme example, the spines merging gradually with the mantle. The spines of neighbouring sibling valves of A. distuns interdigitate loosely and would not appear to perform a very secure linking function (Fig. 14). Nevertheless, many valves are found without spines (Figs 12, 15) proving that such valves are not artefacts due to the spines being broken off since the new sibling valves are still enclosed by the girdle bands. The rim of the valve in Fig. 15 shows a perfectly smooth surface with no indication of broken spines. Fig. 13 shows a valve with broken spines where “scars” can be seen for comparison. The space between the spines is often, but not always, occupied by an areola. The spacing of spines round the rim of the valve is almost, though not precisely regular. This non-sibling heterovalvy is not obviously a linking valve/separation valve heterovalvy similar to that found in other species of the genus where spatulate linking spines form a secure link between sibling valves although examination of live material might prove otherwise. In any case the “separation valve index”, the ratio of separation valves (in A. distuns, valves without spines) to linking valves expressed as a percentage (see Davey & Crawford 1986), is very high (65%) and suggests that chains, if formed at all, are very short. Indeed, the longest chains found in the material comprised 4 cells.

The mantle shows no pronounced “Crawford step” (sensu Ross & Sims 1985) like that found in some other species, e.g. A. lirutu var lucustris (Grunow) Ross (Haworth 1988a, fig. 64), A. ulpigenu (Grunow) Krammer (Krammer 1991a, fig. 12), A. crussipunctutu Krammer (Krammer 1991b, fig. 76; Siver & Kling 1997, fig. llO), A. itulicu (Crawford, unpublished). As in other species of the genus, the surface of the mantle is covered with granules which, at the open edge of the valve, merge to give the appearance of the milled rim of a coin (Figs 10, 12). In other species of Aulacoseiru, the granules are absent from the valve face but in A. distuns they are present as more irregular structures - papillae or rugosities - and usually concentrated towards the centre of the disc (Figs 11, 13). The areolae are more or less circular with deeply embedded vela. The vela in most specimens are still intact and take the form of inverted funnels whose narrow ends point up into the areolae (Figs 18, 19, 20 arrow). They must be attached to the side of the areola but by few points because the wall of the areola appears quite smooth where they are missing.

The robust ringleist is visible on the inner surface and extends some 1/3 of the radius of the valve or more in some specimens (Figs 14, 17-19). Haworth (1988a) prefers the term pseudoseptum but we retain “Ringleiste” which was first used by Muller (1906) for a type of pseudoseptum that seems to be more or less unique to Aulacoseiru and Orthoseira among living diatoms. We use the German word but with anglicised spelling because there is no straightforward English translation.

The rimoportulae in A. distuns are numerous but visible only on the inner surface with the SEM. They are restricted to the area of the mantle next to the ringleist. The rimoportulae are spaced one every 4 or 5 areolae, are of standard form with the base forming part of the ringleist and the slit orientated parallel to it more often than not (Figs 18, 19). The initial valve of the auxospore is, as in other species, devoid of spines. The mantle area is delimited by rows of pores that give way to randomly arranged areolae on the “valve face” (Fig. 21).

DISCUSSION

Krammer (1991a) emphasized the difficulty of identifying A. distuns and its many varieties using the light microscope alone. Only with the SEM is it possible to establish the true nature of the

~

Figs 2, 3. Fig. 2. Light micrograph showing size range and valve outline. Note profile of ringleist in 2 valves, arrows. Fig. 2a, post-auxospore chain with hemispherical initial valve. Scale bars = 10 pm. Fig. 3. Similar field with SEM. Some frustules still have girdle bands attached. Scale bar = 10 pm.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

AULACOSEIRA DISTANS 243

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

244 R. M. CRAWFORD AND Y. LIKHOSHWAY

spines which are vital for identification of all of the small species of Aulucoseiru. A combination of the strong curvature of the mantle and the relatively thick walls means that the spines cannot be seen as easily as in larger species such as A. itulicu. If two sibling valves do come apart then it is possible to see the spines even if some of them are usually broken. Only then is the relationship between the spines and the rows of areolae clearly seen. However, the form of the spines is usually too subtle to be resolved in the light microscope.

Few SEM micrographs of A. distuns have been published. The first appears to have been from material of Kutzing’s, also from Bilin (Crawford 1973, Haworth 1988a,b). This material from the Natural History Museum, London, was not as rich as that found in Berlin and the outside view (Haworth 1988a, fig. 1) depicts a small valve. Nevertheless, the spines are simple and alternate with the pore rows. Krammer provides several LM illustrations of material of A. distuns from Bilin but his SEM micrographs are taken from other sources (Krammer 1991a). Of these, only that shown from Altenschlirf/Hessen in his figs 27 and 39 have simple spines with discrete bases that alternate with the pore rows on the mantle. Krammer (1991a) noted that “Usually, the linking spines arise from a single pervalvar mantle rib (figs 27, 37, 38)” and “Some samples show specimens with linking spines arising from two pervalvar mantle ribs (figs 26, 28).” He appreciates that these latter samples probably do not belong to the nominate variety of A. distuns. His other micrographs either show a slightly different spine shape (eg. Krammer 1991a, figs 37, 38), or spines that are directly opposite a pore row with another pore row lacking a spine to either side. Fig. 72 of Siver & Kling (1997, A. distuns var. distuns) also has this “double rooted” appearance of the spines where the line of the spine can be followed down between pore rows although superficially it does resemble A. distuns. In the Bilin material, the spines are very rarely opposite a row of areolae and never regularly “double rooted”. Whether this is a stable character for A. distuns remains to be seen.

A feature of the mantle that will become useful when other varieties and species are discussed is the presence or absence and the position of the so-called “Crawford Step” - a term coined by Ross & Sims (1985). However, it was Otto Muller who recognised the step produced in one of the sibling valves of Ellerbeckiu (Melosiru) urenuriu (Moore) Crawford by the form of the girdle bands beneath which the new sibling valve is formed (Muller 1883a, b, see also Crawford 1981). It is therefore not only modesty that leads us to propose the term be replaced by “Muller Step”. This feature is absent from all of the A. distuns specimens so far examined in the Bilin material.

The rimoportulae are not easily seen in many species of Aulucoseiru, either in valve or girdle view, yet in A. distuns they can easily be counted in valve view in the light microscope. Krammer illustrates four in his fig. 18 (Krammer 1991a). In reality, they are variable in number depending on the size of the valve. Four is the least observed number but we have seen as many as 12 in larger valves. To our knowledge the only other species of Aulucoseiru with numerous rimoportulae near the ringleist are A. ceretunu and A cunudensis (Hustedt) Simonsen (see Haworth & Sabater 1993). A. islundicu (0. Muller) Simonsen has several rimoportulae but they are scattered freely over the mantle (Le Cohu 1996). When other species have been fully examined, this may be seen as one of the best diagnostic feature for A. distuns.

Another feature that has received less attention in recent descriptions of Aulucoseiru is the velum. In vigorously cleaned material much, if not all, information is lost and we are fortunate that intact vela are still present in the Bilin material yet only on fractured specimens (e.g. Figs 18, 19) can the structure and position of the vela in A. distuns be appreciated. The velum is very similar in

Figs 4-9, LM. Figs 4,5. Several valve views showing areolae. Fig. 6. Girdle view of large valves. Note linking spines between rows of pores, (arrow). Fig. 7. Valve view with 9 rimoportulae along one ringleist. Fig. 8. Three mantle views, one of which has spirally arranged areolae on the mantle, (arrow). Fig. 9. Valve fragment showing clear section through a ringleist (arrow). Scale bars = 10 pm.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

AULACOSEIRA DISTAMS 245

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

246 R. M. CRAWFORD AND Y. LIKHOSHWAY

structure to that of A. buiculensis (K. Meyer) Simonsen where it is also localised to the individual areola although in that species the areola are found only on the mantle (Likhoshway et ul. 1992). This kind of velum is distinctive and has been found in a number of other species of the genus (A. islandicu Le Cohu 1996, fig. 4; unpublished data), Siver & Kling 1997, fig. 91, A. tenellu (Nyg.) Simonsen, but whether it is one extreme of a variation in velum structure hinted at by Crawford (1994) or one of two distinct types remains to be established after other species have been investigated.

Several species of Aulucoseiru have now been shown to have the linking/separation valve heterovalvy (Muller 1903, Florin 1970, Crawford 1979, Davey & Crawford 1986, Le Cohu 1996, Kobayasi & Nozawa 1981) yet this is the first record of such in A. distuns. However, the species appears at present to be unique because of the complete lack of spines on the valve rim. In other species linking spines are frequently so constructed that they interlock securely with those of the sibling, whereas in this material the separation spines are simple, tapering spines that allow the sibling valves to pull apart from one another. The only reported case of a complete absence of spines is in the valves of the initial cell following “germination” of the auxospore (reference Crawford 1975). Davey & Crawford (1986) showed how the length of the chain in Aulucoseiru grunulutu (Ehrenb.) Simonsen was directly related to the separation valve index - the percentage of valves in the assemblage that were separation valves. The higher the index, the shorter the chain. Even if the spined valves are linking valves, which seems unlikely, the chains will be short because of the high index (65%) reported here from the Bilin sample. Indeed lack of any valves that have good interlocking spines suggests that very short chains were the norm in the living assemblage and this is in keeping with the ecology of small Aulucoseiru species like A. distuns so far as it is known. Such species are rarely found in the phytoplankton of larger lakes and are more usually reported from the bottom sediments of smaller, soft/acid-water lakes (Florin 1981, Camburn & Kingston 1986, Haworth 1988a, Siver & Kling 1997). Unfortunately little information is usually given to indicate whether these taxa thrive in the plankton or are seldom suspended from the surface of the sediments and form populations at the sediment/water interface in shallow lakes.

In summary, A. distuns has the following characters in the original material:

Valves 16-20 (35?) wide/8 pm long post-auxospore; smaller valves 4 pm wide/lO pm long. Non-sibling heterovalvy present; “separation” valves have spineless rounded rim, “linking” valves with simple, pointed spines with discrete bases situated between rows of mantle areolae. Areolae circular on mantle and valve face, papillae on valve face. Mantle areolae in straight rows or weakly spiralled to the right (dextrorse). Velum a discrete, inverted funnel with a free end on the inner surface of the valve. Ringleist robust, occluding 1/3-1/2 of the open end of large and small valves respectively. Rimoportulae numerous and found on the inside of the ringleiste.

We are now in a position to evaluate recent illustrations of Aulucoseiru distuns. There is no doubt about the material illustrated with LM by Krammer (1991a) from Bilin of course, but of the SEM figures, only figs 27 and 39, both from AltenschlirfkIessen, are convincing. The other illustrations are doubtful and so too is Aulucoseiru distuns illustrated by Bradbury et ul. (1985). Figs lc, d of Eloranta (1986) are almost certainly not A. distuns and neither are figs 72-74 of Siver &

Figs 10-15, SEM. Fig. 10. Complete parent frustule with 2 series of girdle bands, the epicingulum comprised of 3 bands. Note straight rows of pores. Fig. 11. Single valve with spines, verrucose valve surface and remains of a girdle band. Fig. 12. Frustule comprising 1 linking valve and 1 separation valve with no spines. Note also the markings on valve margin. Fig. 13. Detail of valve face. Fig. 14. Fragment with two valves still united with each other. Note the ringleist. Fig. 15. Two sibling valves as yet still enclosed in the cingula, each without linking spines. Scale bars = 5 p, Fig. 14 =1 pm.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

AUUCOSEIRA DISTANS 247

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

248 R. M. CRAWFORD AND Y. LIKHOSHWAY

Kling because the “root” of each spine runs down either side of a row of areolae and there is a suggestion of a Muller step between valve margin and mantle. At this point we wish to close our comparison with other taxa because we intend to work progressively through the species of Aulucoseiru as they were described and evaluate each in its turn.

It remains to consider the matter of type specimens. There is little reasonable doubt that the material we have been examining here is the same as Ehrenberg used for his drawing (Fig. 1) and for his initial description of the species. He did not designate a holotype specimen - he was not required to do so in his day - and it is not possible to recognise any of the items in his drawings in the mica preparations. Accordingly, we propose to designate a lectotype specimen - the short chain of cells illustrated in Fig. 2a - on a slide that has been marked and deposited at the Ehrenberg collection in Berlin. As the first in a new collection of specimens from Ehrenberg’s original collection this slide is numbered ECO-0001. An isolectotype has also been chosen and this has been deposited at Bremerhaven, BRM Ehr1/37.

ACKNOWLEDGEMENTS

We are extremely grateful to Dr David Lazarus, Museum fur Naturkunde, Berlin for help with the Ehrenberg Collection, to Drs Regina Jahn, Elizabeth Haworth and Hannelore HAkansson for invaluable discussion and finally to Fr. Friedel Hinz for technical help. This is publication No. 1570 of the Alfred Wegener Institute.

REFERENCES

BRADBURY, J. PLAlT, DIETRICH, K.V. & WILLIAMS, J. L. (1985). Diatom flora of the Miocene lake Beds near Clarkia in Northern Idaho. In: Lake Cenozoic History ofthe Pacific North West (J.C. Smiley, ed.), 33-59. American Association for the Advancement of Science.

CAMBURN, K. E. & 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 (J.P. Smol, R. W. Battarbee, R. B. Davis & J. Merilgnen, eds), 17-34.

CRAWFORD, R. M. (1973). Observations on the structure of the frustules of the centric diatom genus Melosira C. A. Agardh. Ph.D. Thesis, University of Bristol, U.K.

CRAWFORD, R. M. (1975). The frustule of the initial cells of some species of the diatom genus Melosira C. Agardh. In: Proceedings of the 3rd Symposium on Recent and Fossil Marine Diatoms, Kiel (R. Simonsen, ed.). Nova Hedwigia, Beih. 53, 37-56.

CRAWFORD, R. M. (1979). Filament formation in the diatom genera Melosira C.A. Agardh and Paralia Heiberg. In: Proceedings of the 5th Symposium on Recent and Fossil Diatoms, (R. Simonsen, ed.), 121-133. Cramer, Vaduz.

CRAWFORD, R. M. (1980). Suggested criteria for the reclassification of the diatom genus Melosira C.A. Agardh. In: Taxonomy of Algae (T.V. Desikachary & V.N. Raja Rao, eds), 671-681. Madras.

CRAWFORD, R. M. (1981). Some considerations of size reduction in diatom cell walls. In: Proceedings of the 6th International Diatom Symposium, Budapest ( R. Ross, ed.), 253-265. Koeltz, Koenigstein.

Figs 16-21, SEM. Fig. 16. Two whole valves, one linking valve, one separation valve. Fig. 17. Inside view showing ringleist. Figs 18, 19. Two fragments showing views of two broken ringleist each with rimoportulae. Fig. 20. Detail of fragment showing vela from inside and in profile within the areola, arrow. Fig. 21. Intact initial valve. Note lack of spines, randomly arranged areolae at the centre and rows near margin of the “mantle”. Scale bars = 5 pn, Figs 19,20 =1 pm.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

AULACOSEIRA DISTANS 249

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2

250 R. M. CRAWFORD AND Y. LIKHOSHWAY

CRAWFORD, R. M. (1994). Transmission electron microscopy and diatom research. In: Proceedings of the 11th International Diatom Symposium, San Francisco (J. P. Kociolek, ed.), 5-19. California Academy of Sciences, San Francisco.

DAVEY, M. C. & CRAWFORD, R. M. (1986). Filament formation in the diatom Melosira granulata. Journal of Phycology, 22, 144150.

EHRENBERG, C. G. (1836). Nachrichten iiber das Vorkommen fossiler Infusioren. Berichte der Kiiniglichen Preussische Akademie fur Wissenschafi, Berlin, 50-54.

ELORANTA, P. (1986). Melosira distans var. tenella and Eunotia zasuminensis, two poorly known planktonic diatoms in Finnish lakes. Nordic Journal of Botany, 6, 99-103.

FLORIN, M.-B. (1970). The fine structure of some pelagic freshwater diatom species under the scanning electron microscope. I. Svensk Botanisk Tidskrijt, 64, 5 1-64.

FLORIN, M.-B. (1981). The taxonomy of some Melosira species. A comparative morphological study. II. Proceedings of the 6th International Symposium on Recent and Fossil Marine Diatoms, Budapest, 1980. (R. Ross, ed.), 43-67. Koeltz, Koenigstein.

HAWORTH, E. Y. (1988a). Distribution of diatom taxa of the old genus Melosira (now mainly Aulacoseira) in Cumbrian waters. In: Algae and the Aquatic Environment (F. E. Round, ed.), 138-167. Biopress, Bristol.

HAWORTH, E. Y. (1988b). Distribution of certain diatom taxa in the water bodies of Cumbria, U.K. Proceedings of the 9th International Diatom Symposium, Bristol (F. E. Round, ed.), 17-28. Biopress, Bristol & Koeltz, Koenigstein.

HAWORTH, E. Y. & SABATER, S. (1993). A new Miocene Aulacoseira species in diatomite from the ancient lake in Cerdanya (NE Spain). Nova Hedwigia, Beih. 106, 227-242.

KOBAYASI, H. & NOZAWA, M. (1982). Fine structure of the freshwater centric diatom Aulacoseira italica (Ehr.) Sim. Japanese Journal of Phycology, 30, 139-146. (In Japanese with English summary).

KRAMMER, K. (1991a). Morphology and taxonomy of some taxa in the genus Aulacoseira Thwaites (Bacillariophyceae). I. Aulacoseira distans and similar taxa. Nova Hedwigia, 52, 89-1 12.

KRAMMER, K. (1991b). Morphology and taxonomy of some taxa in the genus Aulacoseira Thwaites (Bacillariophyceae). II. Taxa in the A. granulata-, italica- and lirata- groups. Nova Hedwigia, 53, 477-496.

KUTZING, F. T. (1 865). Die kieselschaligen Bacillarien oder Diatomeen, Nordhausen. LAZARUS, D. & JAHN, R. (1998). Using the Ehrenberg Collection. Diatom Research, 13,273-291. LIKHOSHWAY, Y.V., YAKUSHIN, A. O., PUZYR, A. P. & BONDARENKO, N. A. (1992). Fine structure of

LE COHU, R. (1996). Further observations and some comments on the fine structure of the centric diatom

MmLER, 0. (1 883a). Das Gesetz der Zelltheilungsfolge von Melosira (Orthosira) arenaria Moore. Berichten

M a L E R , 0. (1883b). Die Zellhaut und das Gesetz der Zelltheilungsfolge von Melosira arenaria Moore.

MULLER, 0. (1903). Sprungweise Mutation bei Melosireen. Berichten der Deutschen Botanischen Gesellschaft.

MmLER, 0. (1906). Pleomorphismus, Auxosporen und Dauersporen bei Melosira Arten. Jahrbucher fur

ROSS, R. & SIMS, P. A. (1985). Some genera of the Biddulphiaceae (diatoms) with interlocking spines. Bulletin

SIMONSEN, R. (1979). The diatom system: ideas on phylogeny. Bacillaria, 2,9-7 1 . SIVER, P. A. & KLING, H. (1997). Morphological observations of Aulacoseira using scanning electron

THWAITES, G. H. K. (1848). On the Diatomaceae. Annals and Magazine of Natural History, 2, 161-172.

the velum and girdle bands in Aulacoseira baicalensis. Diatom Research, 7, 87-94.

Aulacoseira islandica (Bacillariophyceae). Journal of Phycology, 32, 333-338.

der Deutschen Botanischen Gesellschaft, 1 ,3544 .

Jahrbuchefur wissenschaftliche Botanik, 14, 232-290.

21,326-333.

wissenschaftlichen Botanik, 43,4948.

of the British Museum (Natural History) Botany, 13, 227-381.

microscopy. Canadian Journal of Botany, 1807-1835.

Dow

nloa

ded

by [

Uni

vers

ity o

f G

uelp

h] a

t 01:

04 2

7 A

ugus

t 201

2