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COCCONEIS COSTATA VAR.SUBANTARCTICA VAR. NOV., A NEWMARINE DIATOM OFF KERGUELENARCHIPELAGO (SOUTHERN OCEAN,INDIAN SECTOR)Catherine Riaux-Gobin a , Oscar E. Romero b & Adil Y. Al-Handal ca Laboratoire d'Océanographie Biologique, CNRS/UPMC Paris6,UMR7621, FR-66650, Banyuls-sur-Mer, Franceb Institute Andaluz de Ciencias de la Tierra (IACT—CSIC), FacultaddeCiencias, Universidad de Granada, Campus Fuentenueva, ES-18002,Granada, Spainc Göteborgs Universitet, Institutionen för Marin Ekologi, Box 461,SE-405 30, Göteborg, Sweden

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To cite this article: Catherine Riaux-Gobin, Oscar E. Romero & Adil Y. Al-Handal (2009): COCCONEISCOSTATA VAR. SUBANTARCTICA VAR. NOV., A NEW MARINE DIATOM OFF KERGUELEN ARCHIPELAGO(SOUTHERN OCEAN, INDIAN SECTOR), Diatom Research, 24:2, 393-404

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Diatom Research (2009), Volume 24 (2), 393404

COCCONEIS COSTATA VAR. SUBANTARCTICA VAR. NOV., A NEW MARINE DIATOM OFF KERGUELEN

ARCHIPELAGO (SOUTHERN OCEAN, INDIAN SECTOR)

Catherine Riaux-Gobin' Laboratoire d'Oce'anographie Biologique, CNRS/UPMC Paris6, UMR 7621,

FR-66650 Banyuls-sur- Mer, France Oscar E. Romero'

Instituto Andaluz de Ciencias de la Tierra (IACT-CSIC), Facultad de Ciencias, Universidad de Granada, Campus Fuentenueva, ES-18002 Granada, Spain

Adil Y. Al-Handa13 Goteborgs Universitet, Institutionen fdr Marin Ekologi, Box 461,

SE-405 30 Goteborg, Sweden

Keywords: Cocconeis, Kerguelen Archipelago, Southern Ocean, Subantarctic

Cocconeis costutu var. subunturcticu var. nov., a rare taxon from the Kerguelen Archipelago (Southern Ocean, Indian sector), is described using light and scanning electron microscope observations and was compared to related taxa. Apart from the wide-elliptical central area devoid of striae, the raphe valve features highly resemble those of the C. costutu complex: the open cristu marginalis is similar to the one occurring in other varieties of C. costutu, whereas the slightly dissymmetric and hook-like central raphe endings are a distinctive feature. This Subantarctic diatom has a two-layered sternum valve, with alveolate striae consisting of elongated chambers internally open through marginal elliptical wide and regular foramina. On the external side, striae of the sternum valve vary from biseriate to triseriate near the margin, and are not restricted to the foramina location. The resemblance of our new taxon with C. costutu var. puci$cu and C. burleyi, which also possess more or less extended SV chambers, is discussed. The epizoic diatom genera Bennettella and Epipellis, previously assigned to the genus Cocconeis Ehrenberg, also show such alveolate-chambered striae, but are associated with several other very specific features. Several small sized Cocconeis taxa from Antarctic and Subantarctic environments, such as C. costutu var. anturcticu and C. melchiori, show a certain morphological similarity to Cocconeis costutu var. subunturcticu var. nov., but they have marginal short striae on the sternum valve and lack a two-layered sternum valve or chambers.

INTRODUCTION The Kerguelen Archipelago, located between 49"s and 50"s (Fig. l), is a Late Eocene

volcanic system (35 Ma BP) part of the Subantarctic islands, and close to the Antarctic Polar Front (PF) (Park et al. 1993, Moore et al. 1999). This archipelago represents an unique environment for verifying endemism and new morphological emergences because it is far from any terrestrial influence, with the nearest land (Heard Island) being located 440 km southward. Furthermore, even if these Austral islands were located in temperate latitudes, the

' Catherine.riaux-gobin@obs-banyu1s.k Fax: (+33) 04 68 88 95 oromero@ugr.es; Phone (+34) 958 243360 Adil.yousif@marecol.gu.se; Fax: (+46) 03 1-786 27 27

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PF running along the southern part of the archipelago would influence the ecology composition of the marine diatom flora.

i Tasmania

and

Fig. 1. Location of the sampling sites in the Morbihan Bay, Kerguelen Archipelago, Southern Ocean. 1: Port-Aux-Franqais (49"21'S, 70'12'E); 2: mussel beds at Bossiere (49'27' S 69'44'E); 3: Blackney (49'28'S, 70'01'E). Dotted line shows the Antarctic Polar Front according to Park et al. (1998).

Observations of marine diatoms collected on the main island of the archipelago, in intertidal and subtidal sheltered sediments, particularly under a belt of Macrocystis pyrifera (Linnaeus) C. Agardh, showed a highly diverse benthic diatom assemblage (C. Riaux-Gobin pers. obs.), with high contribution from the genus Cocconeis Ehrenberg (Riaux-Gobin & Compere 1996, Riaux-Gobin & Romero 2003, Riaux-Gobin & Compere 2004, Riaux-Gobin et al. 2007). More than 30 Cocconeis taxa were observed, among which several remain unnamed (Riaux-Gobin & Romero 2003).

The valve morphology of the type species Cocconeis scutellum Ehrenberg is characterized by a simple, monolayered valve perforated by uniseriate striae over most of the valve surface and bi- to triseriate striae at the valve margin (Holmes et al. 1982, Romero 1996, De Stefano et al. 2008). The poroid areolae are simple and internally occluded by hymenes showing star-like linear perforations (Mann 198 1, Romero 1996). This simple valve morphology is also shared, among others, with C. californica Grunow, C. costata Gregory and C. stauroneiformis (Rabenhorst) Okuno (Riaux-Gobin & Compkre 1996, Romero 1996, Romero & Rivera 1996, De Stefano et al. 2000, Riaux-Gobin & Romero 2003).

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A higher morphological complexity is encountered in the sternum valve (SV, or P-valve in Round et al. 1990) of some Cocconeis taxa with an alveolate SV which consist of chambers with different degree of development (or alveoli, following the definition by Anonymous 1975) corresponding to an areola or a group of areolae, and opening internally by, usually, one small foramen (Hustedt 1958). These alveoli are particularly well illustrated in Suzuki et al. (2001 a,b,c) and De Stefano & Romero (2005). In the Alveolatae section recently introduced by De Stefano & Romero (2005), both C. contermina Schmidt and C. convexa Giffen possess small alveoli, each corresponding to an areola. A similar arrangement was reported for C. shikinensis Suzuki (Suzuki et al. 2001 b). However, larger alveoli probably resulting from the coalescence of smaller ones were recorded in C. vitrea Brun (De Stefano & Romero 2005), while in C. heteroidea Hantzsch, two adjacent alveoli opened internally through a shared foramen (Suzuki et al. 2001a). Finally in C. barleyi Frankovich & De Stefano, the alveoli are highly developed, occupying the full length of the striae, and internally open by two foramina, the one close to the valve margin being bigger (De Stefano & Romero 2005). In the latter case, the SV is obviously two-layered.

On the other hand, Cocconeis costata var. pacijica Grunow has an axial plate on the internal valve face which delineates more or less widened spaces (Romero & Rivera 1996). This structure may qualify as chambered alveoli even if this taxon was not classified in the Alveolatae section by De Stefano & Romero (2005). Several epizoic taxa previously assigned to Cocconeis and now transferred to the genera Benettella Holmes and Epipellis Holmes (Holmes 1985, Holmes & Nagasawa 1995) show a comparable two-layered SV, with chambered alveoli and foramina, but also with additional characteristics such as alveolate striae on the raphe valve (RV, or R-valve in Round et al. 1990).

Within the Cocconeis costata complex from the Kerguelen Archipelago, Riaux-Gobin & Romero (2003) reported C. costata Gregory var. costata, var. hexugonu Grunow and var. kerguelensis A. Schmidt, as well as an unidentified taxon listed as Cocconeis sp. [aff. C. costata var. antarcticu Manguin]. This latter unnamed taxon relatively rare in the archipelago, was re-examined and described here as a new variety: Cocconeis costata var. subantarctica var. nov. Its morphological affinity with other related Cocconeis taxa exhibiting a two-layered SV in the C. costata complex as well as its comparison to the nominate variety Cocconeis costata var. costata (type BM 947, Greville collection, as reported in Romero & Rivera 1996) and the original description are discussed herein.

MATERIAL AND METHODS The Kerguelen Archipelago (49"20'S, 70'20'E) is a small group of Southern Ocean. The

main island of these subantarctic islands has a large inner bay (Morbihan Bay) and numerous fjords (Fig. l), and was strongly affected by the last glaciation. An intertidal macroalgal belt is well-developed in this area and is mainly composed of Macrocystis pyrifera and Duwillaea antarctica (Chamisso) Hariot. In sheltered fjords, the soft bottom sediment under the dense macroalgal canopy is inhabited by a flourishing macrofauna, with large mussel beds extending into a large part of the Henri Bossibre fjord (site 2, Fig. 1).

Marine diatoms samples were collected during several austral summers, between 1985 and 1992 at numerous sites (Riaux-Gobin & Romero 2003; Table 2) from intertidal and subtidal sheltered sediments on the main island, and particularly under the macroalgal belt, and especially, at three sites in the south-east Archipelago, Port-Aux-Frangais (site 1: 49"21'S, 70"13'E), Bossiere (site 2: 49"27'S, 69'46'E) and Blackney (site 3: 49"28'S, 70'01'E) (Fig. 1). Diatom samples were obtained by scraping the top 0.5 cm of surface sediment with glass containers and the material was preserved in 10% final concentration formaldehyde prior to analysis.

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For light microscopy (LM) observations, the diatom material was prepared by first washing samples with distilled water to remove the salt and then cleaned with 35% hydrogen peroxide (H202) for 30 min. After oxidation of the organic material, cleaned samples were successively rinsed with deionised water. A drop of cleaned diatom material was allowed to settle on a cover slip and air-dried for a few minutes. The mounting medium, Naphrax@, was used to prepare permanent microscopic slides that were examined for diatoms in light microscopy (LM) with phase contrast optics (x100 oil immersion lens, Zeiss Axiophot 2 LM). For scanning electron microscopy (SEM) examinations, a drop of the preserved sample was filtered onto Nuclepore Whatman polycarbonate membranes (13 mm diameter, 1 pm pore size) and rinsed twice with deionised water to remove the salt. Filters were air-dried over night, mounted onto aluminium stubs, coated with gold-palladium in a sputter-coater (EMSCOPSC 500) and examined in a SEM (Hitachi S-4500) operated at 10 kV.

RESULTS Cocconeis costafa var. subanturcficu Riaux-Gobin ef Romero vat-. nov. (Figs 2-25) Synonym: Cocconeis sp. (aff. C. costata var. antarctica Manguin) sensu Riaux-Gobin &

Romero 2003; p. 22, pl. 4, figs 1 4 , pl. 5, figs 1-5; Cocconeis costata var. 1 sensu Riaux-Gobin & Romero 2003; p. 24, pl. 6, figs 1-7.

Valvae ellipticae ad sub-rotundatae, 8.5-19 pm longae, 6.5-13 pm latae, apicibus rotundatis. Sternumvalva convexa. Area axialis recta ad leniter sub-lanceolata, moderate lata (1/9 valva). Striae alveolatae: supeficies exterior punctata, interior apunctata. Striae radiantes et incurvatae ad polos (circa 12 in 10 pm), biseriatae prope sternum, triseriatae ad marginem. Areolae rotundatae et minutissimae ( 3 5 4 0 in 10 pm), interne hymenio cum minutis marginaliter rimulis perforato clausae. Zona hyalina angusta ad marginem locata. Internale tectum cum marginaliter oblongis fenestris. Valvocopula angusta margine undulata.

Raphovalva plana ad leniter concava. Biseriatae striae (1 2-1 7 in 10 pm) non marginem attingentes. Lata area centralis sine stria. Marginaliter crista marginalis, ad polos aperta. Areolae rotundatae et minutissimae (30-36 in 10 pm), interne hymenio cum minutis marginaliter rimulis perforato clausae. Area axialis anguste linearis. Raphe recta, pori centrales leniter axiale dissymmetrici, modice approximati et non deflecti; pori externi terminales simpliciter dilati. Striae paulum visibiles in microscopio optico. Valvocopula lata et tenuis, margine irregularis.

Diagnosis

Habitat sedimenturn marinum Kerguelense.

Description Valves elliptical to sub-round, with rounded apices. 8.5-19 pm long, 6.5-13 pm broad

(Figs 2-1 1, 15,20,21).

Sternum valve (Sv): Externally the valve is gently convex, particularly obvious in tilted view (Fig. 11) with a narrow marginal hyaline rim (Figs 10-12). The axial area is linear to slightly lanceolate, extending up to 1/9 of the valve face. The striae are chambered alveolate, 9.5-17 in 10 pm (Table l), usually biseriate and becoming triseriate near the margins (last 1/3 of the valve, Figs 10-12). The striae are composed of 3 5 4 0 small poroids areolae in 10 pm, which are arranged more or less opposite in the biseriate part of the striae and in quincunx in the triseriate part. The areolae are occluded by poroidal hymen with short linear perforations arranged on a marginal ring (Fig. 13). The striae are radiate and strongly arched towards apices. Internally most of the valve surface is occupied by a wide and slightly concave axial

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COCCONEIS COSTATA VAR. SUBANTARCTICA VAR. NOV. 397

plate (Figs 1 4 1 6 , 18), with large marginal elliptical foramina, or fenestrae, which correspond to the internal openings of the alveoli (Figs 14-18). The internal axial plate is firmly attached to the external valve layer by siliceous thickenings running apically at the position of the axial area and transapically on the interstriae, delineating narrow chambered alveoli on both sides of the sternum (Figs 18, 19). The SV valvocopula is relatively narrow, with slightly wavy proximal pars interior (Fig. 17, arrow).

Raphe valve (RV: The valve is flat in external view and it possesses a shortly elevated and narrow crista marginalis at the junction of the valve and the short mantle, only interrupted at the apices (Figs 20, 21, 23) and a separated row of two to three tiny poroid areolae on the short mantle (Figs 23, 24). A third of the valve surface is ornamented with biseriate striae (Figs 20, 21), 12-17 in 10 pm (Table l), made of 30-35 tiny poroid areolae in 10 pm. A marginal hyaline rim interrupts the striae leaving an isolated row of grouped areolae on small, slightly concave structures, just before the crista marginalis (Figs 15, 21 white arrows). The axial area is narrow, expanding in a transapical wide central area devoid of perforations, except for some isolated poroid areolae near the margin and those grouped just before the crista marginalis. The raphe system consists of two straight branches, with approximate, asymmetrical and hook-like central endings, and sunken and rounded terminal endings (Figs 21-23). Several copulae are present, upon which a cingular band with a ligula (Fig. 23, arrow). RV valvocopula wide, delicate (Fig. 24, white arrow) and irregularly edged (Fig. 16 white arrow, Fig. 15 black arrow) and possibly open (Fig. 23). A fragment of a broken frustule (Fig. 25, detail of Fig. 14, square) showed domed internal hymenes with a marginal ring of tiny perforations, very similar to that observed on the SV (Fig. 13).

Type locality Surface sediment from the mussel bed at site 2, Bossiere (49'273, 69'46'E) Kerguelen Archipelago. Sample "Bossikre mussel bed December 1988" collected by C. Riaux-Gobin, December 1988.

Holotype Slide BM 101340, The Natural History Museum (BM), London, United Kingdom (holotype specimen illustrated in Fig. 6).

Isotypes Slide ZU6/58, Friedrich-Hustedt-Arbeitsplatz, Bremerhaven, Germany (Fig. 8). Slide KER2 from "Bossibre mussel bed 12 1988" in Collection C. Riaux-Gobin, LOB CNRSLJPMC Paris6, Banyuls/mer, France (Fig. 7). Slide AY-CS1, in collection A.Y. Al-Handal, Goteborg University, Marine Ecology, Goteborg, Sweden.

Distribution Specimens of Cocconeis costata var. subantarctica were mostly found in intertidal and subtidal sediments associated with mussel beds, but may have also resulted from an epiphytic association with the macroalgal belt. The abundance of C. costata var. subantarctica can be defined as relatively rare.

Table 1 summarizes the morphologic and morphometric features of C. costata var. subantarctica compared to those of morphologically-related Cocconeis taxa.

DISCUSSION Specimens of Cocconeis costata var. subantarctica are defined by three main valve

features: a two-layered SV with a large internal plate and chambered alveoli. Externally SV striae showed similar ornamentations to those of closely related C. costata complex (Romero & Rivera 1996), while the internal SV is characterized by a wide hyaline, slightly concave, axial plate devoid of areolae with the occurrence of large and elliptical marginally located foramina. Only a short portion of the SV striae can be seen in the interior view through the large foramina. Another specific feature is the transapically developed central area on the RV (occupying up to 2/9 of the valve) which is devoid of areolae, except for a few marginal poroids and the grouped areolae just before the crista marginalis.

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Figs 2-13. Specimens of Cocconeis costata var. subantarctica from the Kerguelen Archipelago. Figs 2-9, LM; Figs 10-13, SEM. Scale bars = 10 pm. Scale bars = 10 pm (Figs 2-9); 5 pm (Figs 10-12); 0.5 pm (Fig. 13). Figs 2, 3. Complete fmstule showing the raphe valve (Fig. 2) and (Fig. 3) the sternum valve (Fig. 3). Figs 4, 5. Same SV at two different focal points. Fig. 6. Holotype specimen, slide BM 1 1.340, Natural History Museum, London. Fig. 7. Isotype specimen, Slide K E N , Collection C. Riaux- Gobin, LOB CNRSWPMC Paris6, Banyuls/mer. Fig. 8. Isotype specimen, Slide ZU6/58, Friedrich- Hustedt-Arbeitsplatz, Bremerhaven, Germany. Fig. 9. Sternum valve. Fig. 10. Part of external sternum valve showing radiate striation and marginal large foramina or fenestrae (arrow). Fig. 11. External view of sternum valve showing striae composed of poroid areolae. Fig. 12. External view of SV apex with the SV valvocopula (arrow). Fig. 13. Areolae with hymenes showing linear perforations arranged on a marginal ring.

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COCCONEIS COSTATA VAR. SUBANTARCTICA VAR. NOV. 399

Figs 14-19. Specimens of Cocconeis costutu var. subunturcticu from the Kerguelen Archipelago. Figs 14-19, SEM. Scale bars = 5 pm (Figs 14, 15); 2 pm (Figs 16, 18); 1 pm (Fig. 19); 0.5 pm (Fig. 17). Fig. 14. Broken fmstule partially showing the RV and the internal axial plate and marginal foramina- fenestrae on the SV, (see Figure 25, magnification of the square-detail of Figure 14). Fig. 15. Broken frustule showing externally the cupules just before the cristu marginalis with grouped areolae (white arrow), and RV broken valvocopula (black arrow). Fig. 16. RV broken valvocopula with an irregular margin (arrow). Fig. 17. Wavy SV valvocopula (arrow) and part of a foramen showing the internal openings of the areolae with hymenes showing a marginal ring of perforations. Fig. 18. Broken SV showing the chambered alveoli (arrow) and marginal foramina. Fig. 19. Broken bi-layered SV showing the siliceous thickening connection of the internal axial plate with the axial area (white arrow) and interstriae (framed arrow).

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Figs 2CL25. Specimens of Cocconeis costata var. subantarctica from the Kerguelen Archipelago. Figs 2&25, SEM. Scale bars = 5 pm (Figs 20,21); 1 pm (Figs 22-24); 0.5 pm (Fig. 25). Figs 20,21. RV external views showing the wide transapical central area devoid of areolae, and the marginal concave structures with grouped (2 to 3) areolae (Fig. 21, arrow) just before the open crista marginalis. Fig. 22. central raphe endings asymmetrical and hook-like. Fig. 23. External slightly expanded terminal raphe ending; note marginal row of tiny areolae (2 to 3 in a group) between the crista marginalis and the border of the mantle, a cingular band with ligula (arrow), and the RV open valvocopula border. Fig. 24. RV valvocopula (arrow) lying below the short mantle margin. Fig. 25. Internal view of hymenate areolae of the RV with short linear perforations arranged in a marginal ring.

Though the morphology of C. costata var. subantarctica from the Kerguelen Achipelago shows specific SV characteristics, the RV by contrast strongly resembles that of present in the Cocconeis costata Gregory 1855 complex. This complex was assigned to the subgenus Pleuroneis by Cleve (1 895; see also discussion in Romero & Rivera 1996).

Cocconeis costatu and morphologically-related taxa have not received much attention since the mid 1990s. Romero & Rivera (1 996) presented LM observations of the C. costuta type and a SEM-illustrated, full description of several taxa pertaining to the C. costata complex, such as C. costata Gregory var. costata, C. costata var. hexagona and C. costata var. pacifica (mostly samples fkom Chilean coastal waters, see also Romero 1995). We were unable to retrieve and examine, particularly with SEM, the original material of C. costatu var. costata and C. paclficu Grunow: nevertheless, as shown by Romero & Rivera (1 996), these taxa also share

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Tab

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. Mor

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Rom

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1996

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402 C. RIAUX-GOBTN, O.E. ROMERO & A.Y. AL-HANDAL

a crista marginalis apparently always present on the RV and more or less raised, biseriate striae with small poroid areolae, a marginal row of smaller and grouped areolae, and a transapical central area laterally expanding in a fascia reaching the valve margin. Similar characteristics are also observed on the RV of C. pinnata Gregory ex Greville, assigned to the subgenus Disconeis sensu Cleve (1895). C. pinnata, however, exhibits very short SV striae (Romero & Rivera 1996) which separates it from C. costata var. subantarctica

The RV of Cocconeis costata var. subantarctica has some particular features: the central area, devoid of areolae, is extremely wide (Figs 20, 2 l), the hook-like central raphe endings are not always symmetrically arranged, and the striae are laterally interrupted, originating a marginal zone devoid of areolae (Fig. 20). Furthermore, the SV in the C. costata complex internally shows coarse and raised interstriae (see also Figs 5,6, 19, 20, 39 and 40 in Romero & Rivera 1996), from which, by their exceptional development and fusion, the internal plate of C. costatu var. subantarctica may have been derived.

Cocconeis costutu var. paclJica whose affiliation with C. fasciolata (Ehrenberg) Brown (see VanLandingham 1968) is still a matter of debate (i.e. different RV of C. fascioluta in Romero 1996), also shows an internal axial plate with an extremely variable width (Rao & Lewin 1976, Romero & Rivera 1996). This variability in the axial plate contributes to more or less developed chamber-like alveoli. The SV stria density in var. paciJica varied geographically from 4-6 in 10 pm to 11-13 striae in 10 pm for specimens recorded in Chile and Argentine, respectively (Table 1) (Romero & Rivera 1996, Sar et ul. 2003).

In contrast to the apparent uniqueness of the axial plate in the SV of C. costata var. paciJica proposed by Romero and Rivera (1 996), this internal morphological feature is also present in other varieties of the C. costutu complex.

Our new variety C. costutu var. subantarcticu was compared with other morphologically related taxa from the southern cold environment. At first glance under LM, the marginal and short structures (i.e. in Figs 3, 5, 8) may resemble the short striae in SV of C. costatu var. antarcticu (Manguin 1960), C. melchiori Frenguelli et Orlando (Frenguelli & Orlando 1958) and C. melchioroides Al-Handal et al. (Al-Handal et al. 2008). However, the more elliptical to sub- round valve outline in C. costuta var. subantarctica distinguishes it from the linear-elliptical valves of the latter Cocconeis species as well as a fully developed striation on the SV covering the whole valve surface of C. costatu var. subantarcticu (Table 1). Furthermore C. costatu var. antarcticu, C. melchiori and C. melchioroides lack an internal axial plate and chambers.

The ornamentation pattern in the SV of Cocconeis costata var. subantarctica also exhibits similarities with the striation of C. cupensis (Cholnoky) Witkowski (Witkowski et al. 2000; basionym C. clundestina var cupensis Cholnoky). Apparently, the striae of C. capensis are not chambered; this feature remains to be described since no SEM views of the RV of C. capensis are available. Furthermore, the RV of C. cupensis (i.e. LM illustration in Witkowski et al. 2000) strongly differs of that of C. costatu var. subantarctica.

In the recently proposed Alveolatae section (De Stefan0 & Romero 2005), the SV internal plate of C. barleyi shows some affinity with our Kerguelen taxon. The large and elliptical marginal foramina bordering the axial plate are very similar to the fenestrae of C. costutu var. subantarctica. The remaining SV and RV features, however, are entirely different.

Similarly the monoraphid epizoic genera Bennettella Holmes and Epipellis Holmes, previously assigned to Cocconeis (Holmes 1985), also show some resemblance to C. costutu var. subantarctica. They all share the chamber-like alveolate striation and the presence of marginal fenestrae on the SV. However, the RV of Bennettella and Epipellis also possess chambered striae (Holmes 1985, Holmes & Nagasawa 1995), which is not the case in C. costuta var. subantarctica .

A complex architecture of the SV characterizes a wide range of Cocconeis taxa. Recent and detailed SEM examination of the valve structure of Cocconeis sensu lato, allowed the

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COCCONEIS COSTATA VAR. SUBANTARCTICA VAR. NOV. 403

proposition of new sections (Alveolatae, De Stefano & Romero 2005) as well as the description of new genera such as Bennettella, Epipellis, Psammococconeis Garcia (Garcia 2001), Amphicocconeis De Stefano et Marino (De Stefano & Marino 2003) and Vikingea Witkowski, Lange-Bertalot et Metzeltin (Witkowski et al. 2000). In spite of the complex SV morphology of C. costata var. subantarctica, its RV is not sufficiently different from those of the other taxa pertaining to the C. costata complex, to support the proposition of a new Cocconeis species. On-going studies on benthic Cocconeis community from the Kerguelen Archipelago will help to better define the morphological relationship in the near future.

ACKNOWLEDGMENTS Funds and logistic assistance in the field were supported by the "Terres Australes et

Antarctiques Franqaises" (TAAF). C. R.-G. thanks "Naturalia and Biologia" and the "Centre National de la Recherche Scientifique" (CNRS) for funding diatom studies in the Kerguelen Islands. We thank the overwintering team members and crew of the RV La Japonaise for field support during the campaigns "Microphythobenthos 85-92" to the Kerguelen Islands. We are grateful to Pierre Compkre (Jardin Botanique National de Belgique, B-Meise) for helping us with the bibliographic research and revision of the manuscript, Dimitri Gorand for SEM assistance (C2M, Via Domitia University, F-Perpignan), to Karen Serieyssol for improving the English, to Sigurd von Boletzky (UMR 7628, F-Banyuls-sur-Mer) for the Latin diagnosis improvement, and Michel Poulin (Canadian Museum of Nature, Can-Ottawa) and an anonymous referee for their comments and for improving the English. We acknowledge Bibliotheca Diatornologica and J. Cramer for giving permission to reproduce figures 9 and 15 which appeared in volume 47.

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Received August 2008; accepted for publication February 2009.

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