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An account of Astartiella species from tropicalareas with a description of A. societatis sp. nov. andnomenclatural notesCatherine Riaux-Gobina, Andrzej Witkowskib & Oscar E. Romeroc

a Laboratoire d'Excellence ’CORAIL’, USR 3278–CRIOBE CNRS–EPHE–Université de Perpignan,Perpignan, Franceb The Faculty of Geosciences, Palaeoceanology Unit, University of Szczecin, Szczecin, Polandc Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Departamento de GeocienciasMarinas, Granada, SpainPublished online: 15 Aug 2013.

To cite this article: Catherine Riaux-Gobin, Andrzej Witkowski & Oscar E. Romero (2013) An account of Astartiella speciesfrom tropical areas with a description of A. societatis sp. nov. and nomenclatural notes, Diatom Research, 28:4, 419-430, DOI:10.1080/0269249X.2013.827590

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Diatom Research, 2013Vol. 28, No. 4, 419–430, http://dx.doi.org/10.1080/0269249X.2013.827590

An account of Astartiella species from tropical areas with a description of A. societatis sp. nov.and nomenclatural notes

CATHERINE RIAUX-GOBIN1∗, ANDRZEJ WITKOWSKI2 & OSCAR E. ROMERO3

1Laboratoire d’Excellence ’CORAIL’, USR 3278–CRIOBE CNRS–EPHE–Université de Perpignan, Perpignan, France2The Faculty of Geosciences, Palaeoceanology Unit, University of Szczecin, Szczecin, Poland3Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Departamento de Geociencias Marinas, Granada, Spain

During a survey of the diatom community associated with coral reefs at Tahiti Island, Society Archipelago, South Pacific, two speciesbelonging to Astartiella Witkowski, Lange-Bertalot & Metzeltin, including A. societatis Riaux-Gobin, Witkowski & Romero sp. nov. aspecies morphologically similar to A. bremeyeri (Lange-Bertalot) Witkowski & Lange-Bertalot, were found from the teguments of a largeHolothuria atra Jaeger (Echinodermata). The second species, A. punctifera (Hustedt) Witkowski & Lange-Bertalot, occurred on nearbymarine sediments. These species were compared with other Astartiella taxa recorded at similar latitudes in the Indian Ocean, namely Juande Nova, Scattered Islands and Mascarene Archipelago. Nomenclatural issues along with the proposed transfer of Achnanthes heterostriataHustedt to Astartiella are discussed.

Keywords: Achnantales, Astartiella societatis sp. nov., black sea cucumber, epizoic diatoms, South Pacific

IntroductionTropical taxa of the genus Astartiella Witkowski, Lange-Bertalot & Metzeltin are common in samples from theSouth Pacific (C. Riaux-Gobin, unpub. data) and the Scat-tered Islands (C. Riaux-Gobin & A. Witkowski, pers. obs.),although this genus is rare in the Mascarene Islands, IndianOcean (C. Riaux-Gobin, unpub. data).

Astartiella is rarely mentioned in diatom surveys, prob-ably due to the difficulty of identifying the taxa under lightmicroscopy (LM). The genus Astartiella has few species(e.g., 13 in Fourtanier & Kociolek 2013) and shares its maincharacteristics with various genera of the family Achnan-thidiaceae. The main characteristics of Astartiella speciesas reported by Moser et al. (1998) and Witkowski et al.(2000) are: heterovalvar, relatively weakly silicified frus-tules, elliptical to lanceolate valves, a flat valve face anda narrow cingulum. The sternum valve (SV) has a struc-ture difficult to resolve in LM and possesses a vestigialraphe. The striae are composed of apically elongate are-olae, similar to Geissleria Lange-Bertalot & Metzeltin butdifferent from Navicula Bory sensu stricto (see diagnosesin Moser et al. 1998). The SV areolae are internally closedby slightly confluent hymenes and have a higher densitythan on the raphe valve (RV). The axial area on the RV isnarrow, the raphe straight and filiform. The terminal raphefissures are curved in the same direction. The RV striae arecomposed of simple and dense areolae internally closed

∗Corresponding author. E-mail: catherine.gobin@univ-perp.fr

(Received 7 June 2012; accepted 17 July 2013)

by round hymenes. There is a stigma (or rarely severalstigmata) in the central area on the secondary side of RV.All currently known Astartiella species are from marine orbrackish environments (Witkowski et al. 2000).

From several lists of Astartiella species availableonline, the most complete to date can be found inFourtanier & Kociolek (2013). It includes 13 entriesfor the genus, with A. bahusiensis (Grunow) Witkowski,Lange-Bertalot & Metzeltin, A. bahusiensoides (Foged)Witkowski, Lange-Bertalot & Metzeltin which is wronglymisspelled in Moser et al. (1998) but was later cor-rected as Astartiella bahuensoides by Witkowski et al.(2000), A. bremeyeri (Lange-Bertalot) Witkowski & Lange-Bertalot, A. bremeyeri var. rostrata (Hustedt) Witkowski &Lange-Bertalot, A. glacialis Witkowski, Lange-Bertalot &Metzeltin, A. ignota (Hustedt) Witkowski & Lange-Bertalot, A. iks Witkowski, Lange-Bertalot & Metzeltin,A. modica (Hustedt) Witkowski & Lange-Bertalot, A. pro-ducta Witkowski, Lange-Bertalot & Metzeltin, A. punc-tifera (Hustedt) Witkowski & Lange-Bertalot, A. stroemii(Hustedt) Bukhtiyarova, A. tenuis (Hustedt) Witkowski &Lange-Bertalot and A. wellsiae (Reimer) Witkowski &Lange-Bertalot.

Hinz et al. (2012) considered Astartiella bahusiensis asinvalid. Furthermore, A. ignota is invalid because the samespecimens were used for typifying both Achnanthes ignotaHustedt and Achnanthes solea Hustedt, the latter having

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priority (Simonsen 1987). Later, Achnanthes solea wasrenamed Achnanthes wellsiae Reimer (Simonsen 1987).Consequently, Astartiella wellsiae is the valid name, whileAstartiella ignota is not valid. Astartiella tenuis is consid-ered a synonym of A. punctifera (Simonsen 1987).

In terms of their morphology, several Astartiella speciesoriginally described as Achnanthes or Navicula taxa aresimilar in shape and striation when observed under LM(see illustrations in Simonsen 1987). High intraspecificmorphological variability is noted for several Astartiellaspecies, such as A. bahusiensis (Witkowski et al. 2000,pl. 52, figs 22–31) and A. bremeyeri (Witkowski et al. 2000,pl. 54, figs 20–24). Specimens supposedly belonging tothe same taxon and found in the type material vary con-siderably in valve outline. For example one specimen ofAchnanthes ignota (Simonsen 1987, pl. 673, figs 10–12)has round apices, while two others have slightly protrud-ing apices (Simonsen 1987, pl. 673, figs 7–9, 13–14). Thenumber of stigmata (thought to be species-specific and mostof the time unique, see original descriptions and illustra-tion in Simonsen 1987) also may vary within a species.Astartiella bahuensoides which was originally describedas Navicula bahuensoides by Foged (1975) showed onestigma, whereas Witkoswki et al. (2000) observed up tothree stigmata. This illustrates the difficulties in an accuratedefinition of Astartiella using LM.

Only two species of Astartiella have so far been exam-ined with electron microscopy. Astartiella bahuensoideswas studied under scanning electron microscopy (SEM)by Moser et al. (1998, pl. 80, fig. 10, RV apex at lowmagnification) and Witkowski et al. (2000, pl. 53, fig. 23,pl. 54, figs 11–13, both RV and SV at low magnification).Astartiella bahusiensis was investigated under transmissionelectron microscopy (TEM) by Moser et al. (1998, pl. 80,figs 1–2) and Witkowski et al. (2000, pl. 52, fig. 22) andunder SEM by Moser et al. (1998, pl. 80, fig. 3, SV striaeat high magnification).

During the Corals and Diatoms off Moorea-Tahiti, Soci-ety Archipelago, South Pacific (COSADIM) 2010 programa new species described here as Astartiella societatis Riaux-Gobin, Witkowski & Romero was found in a Tahiti Islandlagoon sample scraped from the teguments of a largeHolothuria (Halodeima) atra Jaeger. One other Astartiellataxon, A. punctifera was also present on nearby Tahitimarine sediments. These Astartiella taxa were comparedwith those occurring at similar latitudes in the IndianOcean, namely Juan de Nova, Scattered Islands and Mas-carene Archipelago. A new list of valid taxa was proposedand Achnanthes heterostriata Hustedt was transferred toAstartiella.

Material and methodsTahiti Island (17◦52′ S, 149◦56′ W; 1042 km2; Fig. 1),one of the Windward Islands of the Society Archipelago,

Fig. 1. Location of the Society Archipelago in the South Pacificand map of Tahiti Island showing the sampling site known asTombeau du Roi (17◦31.405′S; 149◦31.106′W).

is composed of twin shield volcanoes, which are dated∼1.36 Ma (Cabioch et al. 1999). Tahiti has the highestelevation above sea level of all volcanic islands in theSouth Pacific, with Mont Aora’i at 2241 m. During theCOSADIM 2010 program, an unknown diatom proposedhere as a new Astartiella species was found in the scrapingsof a large specimen of the marine holothurian H. atra nearPointe Honu, Arué District, Tahiti Island (sample Papeete4 Holothuria) in November 2010 (Fig. 1).

The sampling site was located to the north of Tombeaudu Roi (Fig. 1), close to the outlet of a brook (17◦31.405′S, 149◦31.106′ W). Three samples were collected in thisarea: an holothurian scraping (Papeete 4), marine sedimentin the vicinity of the holothurian specimen (Papeete 4a), anda freshwater sample from the brook bed (Papeete 4b). Thespecimen of H. atra living on the coralline gravel bottomwas collected from a depth of 20 cm.

Fifteen samples from the Scattered Islands were alsoexamined, particularly from Juan de Nova Island, a smalltropical coral island between East Africa and Madagascar(17◦03′S, 42◦5′E; 4.4 km2).

Samples were preserved in 10% formaldehyde final con-centration. For the preparation of permanent slides, sampleswere washed with distilled water to remove salts, treatedwith 30% H2O2 for 2 h at 70◦C to digest the organic matter,then washed again in distilled water, alcohol-desiccated andmounted in Naphrax�. Specimens were examined with anOlympus BX41 microscope with differential interferencecontrast optic (DIC), a Canon PowerShot G6 digital cam-era (Instituto Andaluz de Ciencias de la Tierra, Granada,Spain) and a Zeiss Axiophot 200 microscope with DICand Canon PowerShot G6 digital camera (Szczecin Univer-sity, Poland and CRIOBE-University of Perpignan, France).For SEM, preserved uncleaned samples were collected

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Table 1. Physico-chemical variables at 10 cm water depth during sampling at Tahiti Island on 24 October 2010.

Temperature SalinitySample Habitat (◦C) (psu) NO−

2 (μM) NO−3 (μM) PO−

4 (μM) Si(OH)4 (μM)

Papeete 4a Marine 27.3 32.2–33.8 0.11–0.12 5.56–5.61 0.72–0.73 53–56Papeete 4 Holothuria Marine 27.3 32.2–33.8 0.11–0.12 5.56–5.61 0.72–0.73 53–56Papeete 4b Freshwater 26.2 0.1 1.33–1.34 63–64 2.82–3.34 785–786

Notes: NO−3 : nitrate; NO−

2 : nitrite; PO−4 : phosphate; Si(OH)4: silicic acid.

on 1 μm Nuclepore filters, followed by two rinses withdeionized water (MilliQ) to remove salts. The filters wereair-dried and mounted on aluminum stubs before coatingwith gold–palladium alloy (EMSCOP SC 500 apparatus)and examined under SEM (Hitachi S-4500 at PerpignanUniversity operated at 8 and 5 kV and Frankfurt am Mainat 5 or 7 kV).

Although it is a challenge to permanently preserve spec-imens on SEM stubs, these are referenced and kept ina desiccator (CRIOBE-University of Perpignan, France).According to Article 40.5 of the International Code ofNomenclature for algae, fungi and plants (McNeil et al.2012), a holotype SEM image is designated as it shows thebest diagnostic features of the new species and LM slidesare designated as isotypes.

Environmental characteristics are given in Table 1.A YSI 600QS Quick Sample System probe, measur-ing temperature and salinity was used. Nutrient samples[nitrate: NO−

3 , nitrite: NO−2 , phosphate: PO−

4 and silicicacid: Si(OH)4] were filtered on a 0.45 μm GMF What-man syringe-filter to eliminate microalgae and meiofauna,and preserved with HgCl2 (105 ppm) for later analysesin Banyuls-sur-Mer Oceanological Observatory, France.Nutrient concentrations were measured with an Auto-analyser Technicon III following Tréguer & Le Corre(1975).

The terminology follows Anonymous (1975), Ross et al.(1979) and Round et al. (1990).

ObservationsAstartiella species from Tahiti Island, SocietyArchipelagoAstartiella societatis Riaux-Gobin, Witkowski & Romerosp. nov. (Figs 2–6, 12–29; Table 2)Descriptio. Cellulae solitariae. Valvae minutae, oblongae-lineares, apicibus rotundatis, 8.6–10.9 μm longae, 2.0–3.4 μm latae. Raphovalva plana ad leniter concava. Striaeparalleles, circa 38 in 10 μm. Striae aequales et virgaeinterne elevatae. Stigma solitarium praesens unilateraliterin area centralis, axiale elongatum et interne tholiformihymenio closum. Area centralis mediocris, dissymmetricaet latior ad stigmatis latus. Raphe recta filiformis, extremiscentralibus simplicibus, approximatis et leniter deflectis

Figs 2–11. Astartiella species, LM. Figs 2–6. Astartiella soci-etatis sp. nov., isotype slide TAHITI1. Figs 2–3. Sternum valves.Figs 4–6. Raphe valve. Figs 7–8. Astartiella punctifera, slideTAHITI1, raphe valves. Figs 9–11. Astartiella cf. bahuensoides,Juan de Nova, Scattered Islands. Figs 9–10. Complete frustule attwo different foci. Fig. 11. Complete frustule. Scale bars = 10 μm

ad stigmatis latus sed interne non deflectis. Fissurae ter-minales duplo curvatae et ad idem latus deflectae. Areaaxialis anguste linearis. Areolae rotundatae, hymenio deli-cato cum parvis punctis clausea. Plures ampla copulae sinepunctis. Sternumvalva convexa, striae paralleles, circa 53in 10 μm, compluribus et quadrangularibus areolis com-positae. Areolae granulato hymenio clausae. Una apicalisseries ellipticarum areolarum. Virgae equales. Area axialisanguste linearis. Valvocopula aperta.

Description. Cells solitary. Valves small, oblong to lin-ear, with round apices, 8.6–10.9 μm long, 2.0–3.4 μm wide.Raphe valve flat to slightly concave. Striae parallel, ca. 38in 10 μm. Striae equidistant and virgae internally raised.Round areolae closed by delicate hymenes with small pores.One stigma present on one side of the central area, axi-ally elongated and internally closed by a domed hymen.

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Figs 12–17. Astartiella societatis sp. nov. from the type material Papeete 4 Holothuria, SEM external views. Fig. 12. Holotype of acomplete frustule showing the stigma on the raphe valve (arrowhead) and striae on the sternum valve (arrow). Fig. 13. Detail of the centralarea and areolae forming the striae (arrow). Fig. 14. Central area with raphe endings slightly bent toward the stigma. The central area isunilateral. Fig. 15. Whole raphe valve with a marginal row of larger areolae (arrows). Figs 16–17. Apex with detail of the areola hymenes(arrows). Scale bars = 2 μm (Figs 12, 15); 0.6 μm (Fig. 13); 0.5 μm (Fig. 17); 0.3 μm (Figs 14, 16).

Central area not expanded, asymmetrical and wider towardsthe stigma. Raphe straight and filiform, central raphe end-ings simple, close and slightly bent toward the stigma, butinternally coaxial. Terminal raphe fissures doubly hookedand opened towards the same side. Axial area narrowand straight. Sternum valve convex, striae parallel, ca. 53in 10 μm, composed of quadrangular and dense areolae.Areolae closed by granular hymenes. One apical row ofelliptical areolae. Virgae equidistant. Axial area narrow andstraight. Several large cingular bands without perforations.Valvocopula open.

Holotype. Stub 2 13/01/2012, collection C. Riaux-Gobin,CRIOBE-University of Perpignan, Perpignan, France.Holotype specimen illustrated in Fig. 12.

Isotypes. Slides BM101645, Natural History Museum,London, UK, ZU8/38, Hustedt Collection, Bremerhaven,

Germany and TAHITI1, collection C. Riaux-Gobin,CRIOBE-University of Perpignan, Perpignan, France fromthe sample Papeete 4 Holothuria.

Type locality. Sample Papeete 4 Holothuria, Tahiti NuiWest coast, Arué District, North of Tombeau du Roi(17◦31.405′ S, 149◦31.106′ W), collected by scraping aspecimen of H. atra, depth 20 cm, by C. Riaux-Gobin, 24October 2010.

Etymology. The specific epithet is named after the typelocality, the Society Archipelago.

Morphology. The valves of A. societatis are oblong to lin-ear with broad and bluntly rounded apices. The valves showtwo slight constrictions, as illustrated in Fig. 15 (arrows). RVexternal view: The striae have a low number of sub-roundedareolae (on average 4), with a row of larger areolae on the

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Astartiella societatis sp. nov., from Society Archipelago 423

Figs 18–22. Astartiella societatis sp. nov. from the type material Papeete 4 Holothuria, SEM internal views of the raphe valve. Fig. 18.Complete valve showing the stigma (arrow). Fig. 19. Detail of the stigma closed by a finely domed velum (arrow). Fig. 20. Detail of thecentral area with the stigma (arrow) and raised virgae. Note the approximate and coaxial central raphe endings. Fig. 21. Apex with theweakly raised helictoglossa (arrow). Fig. 22. Detail of the finely perforated areola hymenes (arrows). Scale bars = 2 μm (Fig. 18); 1 μm(Figs 20–21); 0.2 μm (Figs 19, 22).

margin and near the raphe (Fig. 13). The areolae are oftenhardly discernible (Fig. 16) and are more pronounced oneroded specimens (Fig. 15). The areolae are closed by finelygranulate hymenate occlusions (Fig. 17). A single axiallyelongated small stigma is located on the secondary side ofthe central area, offset from the central raphe endings. Theraphe is filiform and straight. The cingulum is composed ofup to four bands with straight edges and no apparent perfo-rations. RV internal view: The raphe is slightly elevated withsimple and rather close central endings. Helictoglossae arevery slightly raised. The velum internally closing the stigmais porous similarly to the areola hymenes (Fig. 19). The are-olae are internally closed by hymenes with tiny perforations(Fig. 22). SV external view: The striae are equidistant andbecome only slightly radiate on the apices (Figs 23, 29).The apical areolae are smaller, axially elongated and less

squared than those on the rest of the valve (Figs 26, 29).The SV valvocopula probably lacks fimbriae (Fig. 25, longarrow) and is open at one apex (Fig. 26, arrows). SV internalview: A vestigial raphe is apparent on the axial area nearthe center of the valve (Fig. 25, arrow) and on apices (Fig.27, arrow).

The morphological features of A. societatis are verystable and reproducible, with low standard deviations, par-ticularly in its length/width ratio (Table 2). The species issomewhat similar to A. bremeyeri (Witkowski et al. 2000,pl. 54, figs 20–24), previously illustrated as Achnanthes bre-meyeri Lange-Bertalot (Lange-Bertalot & Krammer 1989,pl. 76, figs 11–12), but the latter is more elliptical (lesslinear) and seems to have denser striae on the apices ofRV (Lange-Bertalot & Krammer 1989, pl. 76, fig. 11;Witkowski et al. 2000, pl. 54, figs 20–21). In LM, it also

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Figs 23–29. Astartiella societatis sp. nov. from the type material Papeete 4 Holothuria, SEM. Fig. 23. External view of whole sternumvalve. Fig. 24. Oblique view of sternum valve showing wide cingulum (arrow). Fig. 25. Detail of the central area of a sternum valve inexternal view showing a vestigial raphe (arrows). Fig. 26. External view of sternum valve showing detail of the apex and cingulum with anopen valvocopula (arrows). Fig. 27. Detail of the apex of a sternum valve in internal view, with raised virgae and vestigial raphe (arrow).Fig. 28. External view of slightly depressed areola hymenes on a sternum valve. Fig. 29. External view of sternum valve showing detailof the apical row of elliptical areolae. Scale bars = 2 μm (Figs 23–24); 0.5 μm (Fig. 25); 0.4 μm (Figs 26–27); 0.3 μm (Fig. 29); 0.2 μm(Fig. 28).

resembles Achnanthidium crassum (Hustedt) Potapova &Ponader, which is broader, has a RV with a symmetri-cally expanded central area and lacks a stigma (Potapova &Ponader 2004, figs 19–27, 44–49; previously illustratedas Achnanthes crassa Hustedt in Simonsen 1987, pl. 325,figs 23–31). Finally in LM, the RV of A. societatis mightbe confused with the freshwater Fallacia enigmatica (Ger-main) Lange-Bertalot & Werum collected from Tahiti(Coste & Ricard 1990, pl. 6, figs 17–19). Although the cen-tral raphe endings of F. enigmatica are curved towards thesame side as in A. societatis (Coste & Ricard 1990, fig. 19),no stigmata can be discerned. The original TEM illustration(Germain 1981, pl. 156, fig. 5) shows a complex doublestriation pattern which might be due to the superpositionof a RV and SV, but suggests no stigma either. Further-more, F. enigmatica is strongly capitate and possesses aconopeum.

Remarks. Astartiella societatis is relatively common onsmall coral sand grains (< 200 μm) found in the holothurianscraping. Although typically epipsammic, the species mayhave an affinity with the particular sheltered environment(the sand grains are firmly embedded and in constantrenewed seawater), or affinity with the particular epizoicbiogeochemical conditions. An obligate epizoic characterremains to be established. Thus far, this species has onlybeen observed as epizoic, in Tahiti, and never in the nearbymarine or freshwater sediments.

Astartiella punctifera (Hustedt) Witkowski &Lange-Bertalot (Figs 7–8, 30–37; Table 2)References. Simonsen 1987, pl. 609, figs 8–15 as Achnan-thes punctifera Hustedt; Witkowski et al. 2000, pl. 52,figs 11–17.

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Astartiella

societatissp.

nov.,fromSociety

Archipelago

425

Table 2. Morphological features and biometric data (range with average and standard deviation in parentheses) of several populations of Astartiella species from Tahiti and Juan deNova islands compared with other populations of the same and related taxa.

A. societatis A. bremeyeri A. punctifera A. punctifera A. cf. bahuensoides A. bahuensoides A. bahusiensis

n 34 n.d. 12 n.d. 21 n.d. n.d.

Valve shape Narrow linear, veryslightly capitate

Variable, fromlinear-elliptical toelliptical, apicesrounded to acute

Elliptical-lanceolateto rhombic, apicesobtusely rounded,sometimes slightlyrostrate

Elliptical-lanceolate,apices obtuselyrounded, sometimesslightly rostrate

Variable, mostlyelliptical-lanceolate,apices rostrate, butoften non-protracted

Elliptical-lanceolate,apices broadlycuneate to broadlyrounded

Elliptical-lanceolateto linear-lanceolate,apices usuallycuneate, obtuselyrounded

Length (μm) 8.6–10.9 10–15 11–24 18–27 11–19 16–29 10–28

(9.8 ± 0.6) (17.2 ± 4.1) (14.4 ± 2.3)

Width (μm) 2.0–3.4 3.5–5.0 4.4–6.9 6–7 6–10 8–11 5–8

(2.7 ± 0.3) (5.9 ± 0.8) (7.6 ± 1.2)

Length/width ratio 3.1–4.9 n.d. 2.4–3.6 n.d. 1.6–2.5 n.d. n.d.

(3.6 ± 0.5) (2.9 ± 0.4) (1.9 ± 0.2)

Stigmata: number,shape, position

1 axially elongate,near the valve center

1 in the center 1 axially elongate, nearthe valve center

1 axially elongate, nearthe valve center

1–3 axially elongate, nearthe valve center

1–3 axially elongate,near the valvecenter

1 axially elongate,near the valvecenter

Central area Small Absent Elliptical Small, rounded Relatively large androunded, but larger onstigma side

Very small Small, unilateral

Axial area Narrow Very narrow Narrow Narrow Narrow Very narrow Very narrow, linear

Central rapheendings

Simple, approximate,curved towards thestigma

Relatively large,approximate

Slightly expanded,approximate

Slightly expanded, wellapart

Slightly expanded Approximate

Striae on RV:Striae in 10 μmorientation

35–45(38.3 ± 3.2)parallel

30 almost parallel inmid-valve, slightlyradiate towardsapices

28–34 (30.1 ± 2.2)slightly radiate

25–28 radiate 30–42 (36 ± 2.7) stronglyradiate at apices

34–36 parallel inmid-valve, radiatetowards apices

25–30 slightly radiate

Axial area on SV Very narrow Very narrow Narrow Very narrow Very narrow Very narrow Very narrow, in themiddle slightlywidened

Striae on SV:Striae in 10 μmorientationAreolae in 10 μm

52.5–66(53.2 ± 3.9)

40 parallel in mid-valve, slightlyradiate at apices

28–39 (34 ± 3.6) onaverage 150

28 parallel or slightlyradiate, delicatelyareolate

29–37 (32.3 ± 2.4)parallel in mid-valve,slightly radiate at apiceson average 120

21–24 parallel 30–36 slightly radiate

115–120Terminal raphe

fissuresDoubly hooked towards

primary siden.d. Hooked in the same

directionn.d. n.d. n.d. n.d.

Distribution Tahiti, South Pacific Gulf of Gdansk, NorthSea

Tahiti and Moorea, SouthPacific

Cosmopolitan Juan de Nova,Mozambique Channel

Tanzania, Oman andGulf of Aden

Cosmopolitan

Reference This study Moser et al. (1998) This study Moser et al. (1998) This study Moser et al. (1998) Moser et al. (1998)

Notes: n: number of specimens observed with SEM; n.d.: no data.

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Figs 30–37. Astartiella punctifera from Tahiti and Moorea islands, SEM external views. Figs 30, 33–34. Raphe valves. Note the variationin shape. Fig. 31. Sternum valve. Fig. 32. Apex of a sternum valve with open valvocopula (arrow). Figs 35–37. Raphe valves showingcentral area with stigma. Note the small areolae (arrow). Scale bars = 4 μm (Figs 30–31, 33–34); 1 μm (Figs 35–37); 0.5 μm (Fig. 32).

Synonym. Astartiella tenuis (Hustedt) Witkowski &Lange-Bertalot.

Morphology. The valves are elliptical (Figs 30–31) tolinear-elliptical (Figs 33–34), more or less wedge-shapednear the ends, with rounded, barely drawn-out apices. Nofascia present on the RV. The areolae on RV are irregular insize (Figs 35, arrow, 36–37). The central area is relativelywell developed (Fig. 35). The striae on SV are composed ofnumerous narrow areolae (ca. 150 in 10 μm, Fig. 32). Thevirgae on SV are slightly elevated and wide (Fig. 32). Thecingulum is composed of up to 5 bands with an open SVvalvocopula (Fig. 32, arrow).

Astartiella punctifera was rare on Tahiti Island andobserved in the holothurian scrapings along with A. soci-etatis and in marine sediments (Figs 30–37), and was alsopresent at Moorea Island. It has a slightly higher stria den-sity than the type (Table 2). Astartiella punctifera is largerthan A. societatis (Table 2) and has more elliptical valves,with a single transapically elongated stigma (Figs 35–36).Although size and stria density are relatively constant (seeSD in Table 2), the shape varies. The striae are radiateall over the valve in some specimens (Fig. 30), but areradiate only at the apices in others (Figs 33–34). Thesedifferent morphologies suggest multiple varieties, but moreobservations are required to confirm this assumption. Astar-tiella wellsiae has a less elliptical (more linear) shape than

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Astartiella societatis sp. nov., from Society Archipelago 427

Figs 38–41. Astartiella cf. bahuensoides from Juan de Nova, Scattered Islands, SEM external (Figs 38–39, 41) and internal views (Fig.40). Figs 38–39, 41. Raphe valves showing fascia (arrows) and high variation of shape. Fig. 40. Raphe valve with stigma system (a centralinternally opened stigma and two closed satellite structures, arrows) and raised central virgae. Scale bars = 5 μm (Figs 40–41); 3 μm (Figs38–39).

A. punctifera, and the Tahiti specimens illustrated here mayrepresent this species (Figs 33–34).

Astartiella species from the Western Indo-Pacific BasinAstartiella cf. bahuensoides (Foged) Witkowski, Lange-Bertalot & Metzeltin (Figs 9–11, 38–55; Table 2; specimensfrom Juan de Nova, Scattered Islands)

References. Witkowski et al. 2000, pl. 52, figs 20–21,pl. 53, figs 23–37, pl. 54, figs 11–19. Navicula bahuensoidesFoged 1975, pl. 19, figs 8–9.

This diatom is smaller than A. bahuensoides (11–19 μmlong versus 16–29 μm in the type) and stria density on SV ishigher (29–37 versus 21–24, Witkowski et al. 2000). Thereis also considerable variability in the frustule shape fromelliptical to broadly elliptical with rounded apices (Figs 39,53), to lanceolate with strongly protracted ends (Fig. 41).The RV is similar to that of A. bahuensoides (Foged 1975,Witkowski et al. 2000).

The fascia is very apparent (Figs 9–11, 38–39). Exter-nal views show three central slightly concave striae on bothsides of the valve (Figs 38, arrows, 39), with less-markedareolae than on the rest of the valve. Internally, these arebordered by two raised virgae (Fig. 40). The slightly radi-ate striae are uniseriate (Fig. 40). The RV areolae (35–40 in

10 μm) are externally occluded by hymenes delicately per-forated by regularly arranged rounded pores, 11–12 nm indiameter (Fig. 44). The internal view of RV shows domedareola hymenes (Fig. 40) with scattered rounded perfora-tions (Fig. 48, arrow). Near the margin, the areolae areflame-shaped (Figs 38–39, 42). The areolae adjacent to theaxial area are externally very deep-set (Fig. 43, arrow). Thestigmata (often in a group of three: a central stigma flankedby two smaller satellite openings) are situated in the prolon-gation of the areolae (Fig. 46) or, more often slightly offset,on one side of the central area (Figs 45, 47). The centralstigma is larger than its two satellite structures and is openinternally, whereas the two satellite structures are closed(Fig. 40, arrows).

On the SV, the striae are parallel in the middle of thevalve to slightly radiate at the apices and composed ofdense axially elongated areolae which are concave and oftenslightly oblique internally (Fig. 52, arrow). The areolae arewell-separated and their hymenes are not confluent (Fig.55). A vestigial raphe is often present in the middle of thevalve (Fig. 51, arrows), but also on the apices (Fig. 54,arrow). The SV valvocopula is open (Fig. 54).

Astartiella cf. bahuensoides is abundant in the Mozam-bique Channel (i.e., relatively frequent in Juan de NovaLagoon) although apparently absent in the Mascarenes (C.Riaux-Gobin, pers. obs.), suggesting a disjunct distribution

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Figs 42–49. Astartiella cf. bahuensoides from Juan de Nova, Scattered Islands, raphe valve in SEM external (42–47, 49) and internalviews (Fig. 48). Fig. 42. Expanded central area (arrow). Fig. 43. Marginal row of strongly deep-set areolae near the raphe (arrow). Fig.44. Rounded areolae positioned more or less in quincunx, with finely perforated hymenes. Figs 45–47. Detail of the stigma system, oftencomposed of a long central stigma (arrow) with two satellite openings. Fig. 48. Areolae with finely perforated hymenes. Fig. 49. Apexwith chiseled marginal areolae (arrow) and doubly hooked terminal raphe fissure. Scale bars = 3 μm (Fig. 42); 0.5 μm (Figs 45–47, 49);0.3 μm (Fig. 48); 0.2 μm (Fig. 44).

over the Indian Ocean. So far, A. cf. bahuensoides has notbeen found in the Society Archipelago.

Remark. An invariable characteristic of A. cf. bahuen-soides is the presence of a fascia which has not always beenshown previously (Foged 1975, Witkowski et al. 2000).

A new Astartiella combinationAstartiella heterostriata (Hustedt) Riaux-Gobin,Witkowski & Romero comb. nov.

Basionym. Achnanthes heterostriata Hustedt 1952, BotaniskaNotiser, p. 388, figs 85–86.

Remark. This new combination is proposed based onthe observation of a stigma in Achnanthes heterostriata(Simonsen 1987, pl. 583, figs 25–28).

DiscussionUltrastructural characteristics of Astartiella speciesOur observations revealed several new details of the ultra-structure of Astartiella species:

(1) The hymenes occluding the SV areolae are individ-ual and not confluent as described in the originaldiagnosis (Moser et al. 1998). The RV areolae areoccluded by finely perforated hymenes. The areolahymenes on SV are covered by rough granules.

(2) A key characteristic of the genus is the pres-ence of the simple or complex stigma on theRV. The solitary stigma in A. societatis is closedinternally by a domed velum with aligned poressimilar to the hymenes of adjacent areolae (Fig.19). In A. cf. bahuensoides the central stigma isnot occluded internally, whereas the lateral onesprobably are (Fig. 40, arrows).

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Astartiella societatis sp. nov., from Society Archipelago 429

Figs 50–55. Astartiella cf. bahuensoides from Juan de Nova, Scattered Islands, sternum valve in SEM external (Figs 50–51, 53–55) andinternal views (Fig. 52). Figs 50, 53. Whole valve, weakly silicified. Fig. 51. Striation consisting of apically elongated areolae with narrowvirgae. A vestigial raphe is shown (arrows). Fig. 52. View of depressed areolae (arrow). Fig. 54. Apex with vestigial raphe (arrow) andopen valvocopula. Fig. 55. Striae with occluded areolae. Scale bars = 4 μm (Fig. 50); 3 μm (Fig. 53); 1 μm (Figs 51, 54); 0.5 μm (Fig.52); 0.2 μm (Fig. 55).

In the suborder Biraphidineae several genera bear stig-mata, but within the order Achnanthales this structure isfound only in the genus Astartiella. The morphology ofthe stigmata is variable among diatom genera. In Reime-ria Kociolek & Stoermer, a stigma is unoccluded, bothinternally and externally (Round et al. 1990), whereas inGomphoneis Cleve one or several stigmata open internallyby a narrow slit (Round et al. 1990). In Luticola D.G.Mann and Olifantiella Riaux-Gobin & Compère, the stigmaextends internally into a structured process (Round et al.1990, Riaux-Gobin & Compère 2009). In Cymbella C.Agardh, the stigmata are internally occluded by convolutedinternal occlusions (Round et al. 1990), whereas in Didymo-sphenia Schmidt they open internally through convolutedspongy bosses of silica (Round et al. 1990). The structure ofstigmata is genus-specific, but their function is unclear.

(3) The cingulum is composed of several apparentlyimperforated bands, with at least one open band(the SV valvocopula).

(4) A vestigial raphe is present on the SV of severalAstartiella species.

Morphological variability and discrimination ofAstartiella speciesWith its very specific and stable characteristics, A. soci-etatis is easy to identify in SEM (Table 2), but this is notthe case for several other taxa. Astartiella bahuensoides,to date only found in Tanzania, Oman and Gulf of Aden,seems to have high morphological variability (Witkowskiet al. 2000). Astartiella cf. bahuensoides is reported fromJuan de Nova Island, Mozambique Channel, which is geo-graphically close to the type locality of A. bahuensoides.However, A. cf. bahuensoides has features slightly differ-ent from those of A. bahuensoides (Table 2) and moleculardata would help to determine whether they are conspecificor not. Likewise, its shape is highly variable.

Astartiella punctifera specimens observed in this study(Figs 30–34) possibly include several varieties, even

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species. The specimens illustrated in Figs 30–31 are ellipti-cal, with a large central area (Fig. 30) and central raphefissures well apart, whereas the specimens illustrated inFigs 33–34 are rhombic, with reduced central area andapproximate central raphe fissures. Some morphologicalconvergences exist between taxa such as A. punctifera,Achnanthes solea, A. heterostriata (close to A. modicabut with parallel SV striae), A. modica (with a coarserstriation than the above mentioned taxa) and to a lesserextent A. bremeyeri var. rostrata. The latter taxon is con-sidered a synonym of A. bahusiensis by Lange-Bertalot &Krammer (1989). For the discrimination of all these taxa itwould be of interest to reinvestigate their type materials bySEM.

AcknowledgementsWe acknowledge Dimitri Gorand (C2M, University of Perpignan)for SEM assistance, Louise Oriol (Banyuls-sur-Mer Oceanologi-cal Observatory) for the nutrient data, Pierre Compère (NationalBotanic Garden of Belgium, Meise) for the revision of the Latindiagnosis, Kevin McCartney (University of Maine) and SuzieMills (USR 3278 CRIOBE EPHE-CNRS) for English revisions.Marina Potapova, Michel Poulin and two anonymous reviewersgreatly improved the manuscript. We also thank Terres Australeset Antarctiques Françaises (TAAF) who allowed the participa-tion of C R-G and AW on the EPARSES 2009 expedition. USR3278 CRIOBE EPHE-CNRS is acknowledged for funding diatomstudies at Tahiti Island. The Polish Ministry of Science & HigherEducation provided funds through grant NN 306 4 68538 and OERwas partially funded by the Spanish Council of Research (CSIC).This work has been presented at the 22nd International DiatomSymposium in Ghent, Belgium in August 2012.

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