Aulacoseira westfjordensis Van de Vijver, L.Willems & Pottiez, 2025

Vijver, Bart Van De, Willems, Luna, Haan, Myriam De, Ballings, Petra & Pottiez, Margaux, 2025, Aulacoseira westfjordensis, a new centric diatom species from Iceland (Aulacoseiraceae, Coscinodiscophyceae), Phytotaxa 712 (1), pp. 75-80 : 76-78

Aulacoseira westfjordensis Van de Vijver, L.Willems & Pottiez , sp. nov. ( Figs 1–28 )

Description:—Frustules cylindrical, rectangular in girdle view, connected to each other with linking spines forming long colonies ( Figs 1–8, 22 ). Linking spines long, fine, attenuate, with anchor-shaped tip and irregular acute outgrowths on the side ( Figs 22–26 ). Cingulum composed of numerous open girdle bands entirely perforated by very fine pores ( Fig. 21 ). Copulae ligulate. Valvocopula broad, with fimbriate advalvar margin ( Fig. 21 ). Mantle fairly high, 4–6 µm in height. Mantle striae fine, composed of small, irregularly rounded to rectangular areolae, arranged in well separated rows, spiraling in the abvalvar part of the mantle, straight in the upper part closest to the valve face/mantle junction ( Figs 22–24 ). Areola density per row ca 20 in 10 μm (n=10). Between the mantle areolae, numerous small, siliceous plaques present ( Figs 22, 23 ). Collum, the lowermost part of the mantle, lacking areolae, narrow, reaching at most 5% of the total mantle height ( Fig. 22 ). Collum entirely covered by narrow, raised ribs composed of individual small silica granules ( Figs 22–24 ).

Valves circular, 7.0–12 μm in diameter (n=20). Discus flat, entirely devoid of areolae. Only marginal areolae present ( Figs 25, 27 ). Spines located between the marginal areolae, placed on the valve face edge ( Fig. 25 ). Internally, very shallow Ringleiste visible ( Figs 9 , arrow, 28). Areolae covered by individual vela ( Fig. 28 ).

Type:— ICELAND.Westfjords (Vestfirðir), River at Mjóifjörður, sample W 022 (65°53’11.01”N, 22°50’56.71”W), coll. date 09. VI.2023, leg. B. Van de Vijver (holotype slide BR-4890= Fig. 10 , isotype slide 454, University of Antwerp, Belgium).

PhycoBank registration:—http://phycobank.org/105731

Etymology: —The specific epithet refers to the geographical location (Westfjords, Vestfirðir in Icelandic language) where the new species was found.

Ecology & associated diatom flora:—Sample W022 was collected from submerged stone scrapings in the weakly acid river flowing into the Mjóifjörður fjord in the Westfjords in Iceland. It was dominated by several Psammothidium species, Meridion circulare ( Greville 1822: 213) C. Agardh (1831: 40) , Hannaea linearis ( Holmboe 1899: 31) Álvarez-Blanco & S.Blanco (2013: 147) , Odontidium mesodon ( Ehrenberg 1839: 57) Kützing (1849: 12) , Tabellaria flocculosa ( Roth 1797: 192) Kützing (1844: 127) , Rossithidium pusillum (Grunow in Cleve & Grunow 1880: 23) Round & Bukhtiyarova (1996: 351) and several, at present unidentified Gomphonema , Staurosira and Fragilaria species. According to Lange-Bertalot et al. (2017), most of these species are typical for nutrient-poor, slightly acid, soft-water rivers and lakes, and several of them have a boreal distribution such as H. linearis ( Álvarez-Blanco & Blanco 2013) . The species was observed in several other brooks and rivers in the Westfjords showing its broader distribution in this region (Willems et al. unpubl. res.).

Kulikovskiy et al. (2010) most likely observed the species in a Sphagnum bog in Mongolia. Due to confusion with similar species ( A. septentrionalis , A. helvetica ) its actual distribution is therefore probably obscured.

Figures

FIGURES 1–28. Aulacoseira westfjordensis Van de Vijver, L.Willems & Pottiez, sp. nov. LM and SEM pictures taken from the holotype slide (BR-4890, Westfjords, Iceland, sample W022). Figs 1–8. LM views of the frustules in girdle view connected to each other. On Fig. 3 the spines are clearly sticking out (arrow). Fig. 9. LM view of a valve in valve face view focusing on the Ringleiste (arrow). Figs 10–19. LM views of a size diminution series. Fig. 20. SEM external view of several frustules connected to form a long colony. Fig. 21. SEM external view of the open, perforated girdle bands. Note the valvocopula. Fig. 22. SEM view of two valves connected by linking spines. Fig. 23. SEM external detail of the linking spines. Note also the structure of the areolae and the large siliceous plaques. Fig. 24. SEM external view of a valve in girdle view with a good observation of the spines, the mantle edge and the areolae. Fig. 25. SEM external valve face view showing the marginal areolae and the location of the spines on the valve face/mantle junction. Fig. 26. SEM external detail of the linking spines. Fig. 27. SEM external valve face view with eroded valves and distinct marginal valve face areolae. Fig. 28. SEM internal view of an entire valve. Note the areola occlusions and the shallow Ringleiste. Scale bars represent 10 µm except for Figs 22, 24 & 25 where scale bar = 1 µm.