Aulacoseira glubokoyensis Oaquim, Moser, Evangelista & Van de Vijver, 2017

Oaquim, Anna Beatriz Jones, Moser, Gleyci A. O., Evangelista, Heitor, Licínio, Marcus Vinícius & Vijver, Bart Van De, 2017, Aulacoseira glubokoyensis sp. nov. (Bacillariophyceae), a new centric diatom from the Maritime Antarctic region, Phytotaxa 328 (2), pp. 149-158 : 150-151

Aulacoseira glubokoyensis Oaquim, Moser, Evangelista & Van de Vijver sp. nov. ( Figs 1–29)

LM ( Figs 1–18):—Frustules in chains ( Fig. 1) of up to fourteen cells. Valve diameter 7.5–12.0 μm (mean 10.11 ± 1.04 μm; n = 25), mantle height 4.5–6.0 μm (mean 5.2 ± 0.4 μm; n = 25). Ratio of mantle height to diameter between 0.5 and 0.7 (mean 0.6 ± 0.1; n =25). Density of pervalvar rows of areolae on the mantle: 15–16 in 10 μm (n = 25).

SEM ( Figs 19–29): Mantle: Girdle bands entirely perforated by very fine pores, rarely visible even in SEM, but similar to those found in other Aulacoseira species ( Crawford & Likhoshway 1999) ( Fig 19). Collum, the lowest part of the mantle lacking areolae, narrow, max. only 5% of the total mantle height ( Figs 20, 21, 23), entirely covered by narrow, raised ribs ( Figs 21, 23). Some valve mantles showing a typical “Muller Step” (sensu Muller 1884 and Crawford & Likhoshway 1999) ( Figs. 20, 21, 23). Between the mantle areolae, numerous small, siliceous plaques present ( Figs 21, 22). Areolae: Mantle composed of relatively small, irregularly rounded areolae, arranged in well separated rows, oblique to spiraling ( Figs 20, 21, 23). Areola density per row ranging between 19 and 21 in 10 μm (n = 10). Row of areolae continuing uninterruptedly over the mantle/valve face margin onto the valve face ( Fig. 23). Internally, areolae on both mantle and valve face covered individually by irregular rosettes of vela ( Crawford & Likhoshway 2002) ( Figs 28, 29). Discus: generally flat, never verrucose lacking papillae ( Figs 24, 25). Transition to the mantle weakly depressed between the spines ( Fig. 25). Discus usually showing one or two marginal rings of areolae. Inner row of areolae usually composed of much smaller, rounded pores. Areolae between the spines much larger ( Fig. 24). Occasionally, several irregularly scattered areolae present on the discus ( Figs 10, 16, 17, 25). Ringleiste: Ringleiste very broad, covering almost half of the valve width ( Fig. 26) located at the junction between the areolated mantle and the collum ( Fig. 27), protruding into the cell with a thickened rim ( Figs 26, 27). Spines: At the junction of mantle and valve face, a marginal ring of well-developed linking spines present, separated from each other by one areola ( Figs 20, 21, 22, 23, 24, 25). Spines straight to irregularly cruciform to dendritically shaped ( Fig. 22). Typical separation valves with characteristic long, pointed separation spines never observed. Rimoportula: at least two rimoportula observed (number of valves checked: 50), situated on the Ringleiste ( Figs 28, 29, see arrows). Rimoportulae clearly stalked, never overlapping the Ringleiste ( Fig. 29).

Remarks:—It was impossible to determine the exact length of complete chains due to the fragmentation of subfossil material.

Type:—Fildes Peninsula, King George Island, South Shetland Islands, sample P04-Artigas, (leg. A. Oaquim), collection date 25/03/2013 (holotype BR!, slide no. 4490, isotype R! slide no. 232252, Herbarium of Museu Nacional, Brazil, isotype PLP! slide no. 328, University of Antwerp, Belgium). Figure 11 represents the holotype.

Etymology: —The specific epithet glubokoyensis refers to the old name of Profound Lake, (Lago Glubokoe or Ozero Glubokoye), on Fildes Peninsula, the type locality of the species.

Ecology & Distribution:—The new species is at present only known from the sediment core taken from Profound Lake, the type locality on King George Island. The layers in which A. glubokoyensis was frequently observed are dominated by several Psammothidium taxa such as P. abundans (Manguin in Bourrelly & Manguin 1954: 19) Bukhtiyarova & Round (1996: 22), P. subatomoides (Hustedt in Schmidt et al. 1936: pl. 404, fig. 33–35) Bukhtiyarova & Round (1996: 13–14) and P. confusoneglectum Kopalová et al. (2016: 9) . Other common taxa include Diatomella balfouriana Greville (1855: 259) , Fragilaria sp. , Stauroforma exiguiformis ( Lange-Bertalot 1993: 45–46) Flower et al. (1996: 53–54) , Planothidium renei (Lange-Bertalot & Rol. Schmidt in Schmidt et al. 1990: 64–65) Van de Vijver in Van de Vijver et al. (2002: 102) and Cavinula pseudoscutiformis (Hustedt in Schmidt et al. 1930: pl. 370, fig. 46) D.G.Mann & Stickle in Round et al. (1990: 665). This species composition is typical for aquatic conditions with a significant influence of a wet, submerged or surrounding moss vegetation ( Zidarova et al. 2016).