Gomphonema maritimo-antarcticum Van de Vijver, Kopalová, Zidarova & Kociolek, 2016

Vijver, Bart Van De, Kopalová, Kateřina, Zidarova, Ralitsa & Kociolek, J. Patrick, 2016, Two new Gomphonema species (Bacillariophyta) from the Maritime Antarctic Region, Phytotaxa 269 (3), pp. 209-220 : 212-214

Gomphonema maritimo-antarcticum Van de Vijver, Kopalová, Zidarova & Kociolek , sp. nov. ( Figs 22–74)

LM ( Figs 22–61): Frustules in girdle view almost rectangular, weakly clavate with a slightly narrower footpole. Valves lanceolate to rhombic-lanceolate, often asymmetrical to the apical axis. Headpole either not or only weakly protracted, acutely rounded in larger specimens, rostrate to truncated in mid-size to smaller specimens. Footpole always acutely rounded, pointed. Valve dimensions (n=100): length 20–50 μm, width 4.5–7.0 μm. Axial area rather narrow, broader in longer specimens, 1/4–1/5 of the total valve width, linear to linear-lanceolate, not widening towards the central area. Central area asymmetrical, rectangular to slightly wedge-shaped with one shortened stria on one side and one normal stria on the other side. Stigmoid rounded, at the end of the central stria, slightly separated from the last areola. Raphe clearly lateral, undulate. Proximal raphe endings deflected, weakly expanded. Distal raphe fissures hooked. Striae radiate to weakly moderate, becoming parallel near the headpole, 12–14 in 10 μm, more densely spaced near the head- and foothpole (up to 18 in 10 μm). In smaller specimens striae even parallel throughout the entire valve. Areolae weakly discernible in LM. SEM (66–74): Striae uniseriate composed of “C”- to “3”-shaped areolae (Figs 64, 66, 67, 70). Occasionally striae biseriate due to doubling of the areolae ( Fig. 67). Striae continuing uninterruptedly onto the mantle, terminating in one small rounded areola (Fig. 62). Mantle edge forming a relatively broad hyaline zone (Fig. 62). Mantle of initial valves bearing a large series of rounded areolae per stria (Fig. 63). Girdle bands perforated by one series of rounded pores (Fig. 62). Footpole with a hyaline tip (Fig. 64). Large apical pore field present at the footpole composed of up to 8 rows of relatively large pores (Figs 62, 64, 66, 67). Initial valves and larger specimens showing an (often reduced) apical pore field at the headpole (Figs 63, 64, 65). Apical pore field bisected by the distal raphe fissures ( Fig. 68). External raphe branches undulate with clearly deflected external proximal endings terminating in enlarged, drop-like pores ( Figs 66, 67, 73). Distal raphe fissures (strongly) hooked, almost not continuing onto the mantle ( Figs 69, 72). External stigmoid opening rounded to transapically enlarged (including in initial valves), clearly larger than the areolae, weakly separated from the last areola of the central stria (Figs 64, 66, 67, 73). Foot- and headpole with small pseudoseptum ( Fig. 68). Internally, central nodule weakly raised. Internal proximal raphe endings clearly distant from each other, distinctly recurved ( Fig. 71). Distal raphe endings terminating on small helictoglossae ( Fig. 68). Striae internally bearing vimines, oriented perpendicularly to the striae. Doubling of areolae occasionally visible ( Fig. 74). Areolae internally with round foramina. Internal stigmoid opening slit-like, well separated from the last areola in the central striae ( Fig. 71).

Type:— LIVINGSTON ISLAND ( SOUTH SHETLAND ISLANDS). Byers Peninsula, sample BY15 (62° 39’ 24.1” S, 61° 06’ 48.9”), B. Van de Vijver, 11 January 2009 (holotype BR! slide no. 4445, isotype PLP! slide 300, University of Antwerp, Belgium).

Ecology and distribution: — Gomphonema maritimo-antarcticum is a very common diatom in large lakes and ponds of James Ross Island and the South Shetland Islands, including Livingston Island and other major islands (King George Island and Nelson Island, Zidarova, pers. obs.). Large populations have been found in slightly to very alkaline lakes, ponds and streams (pH 7.78–9.30) with a low to moderate conductivity (<33000 μS/cm). Based on the available iconographic data from earlier studies in other areas in Antarctica, the species might also be present further south, on Horseshoe Island, Antarctic Peninsula ( Wasell & Håkansson 1992, figs 28–33, 36, 84, as Gomphonema cf. angustatum / parvulum ) and on the Antarctic Continent ( Sabbe et al. 2003, p. 237, fig. 50, as Gomphonema sp. ).

Etymology: — The specific epithet refers to the biogeographical distribution area of the new species: Maritime Antarctic Region. The hyphen can and should be maintained in the species name based on art. 60.9 of the International Code of Nomenclature for algae, fungi and plants ( McNeill et al. 2012).

Taxonomic remarks: — Shorter valves of Gomphonema maritimo-antarcticum with a more rhombic-lanceolate outline can be confused with G. punae Lange-Bertalot & Rumrich in Rumrich et al. (2000: 140) and G. pseudoclavatum Lange-Bertalot & Reichardt in Lange-Bertalot et al. (1996: 92). Both taxa were described from southern Chile but can be separated from G. maritimo-antarcticum . Both Chilean taxa have a different striation pattern with equidistant striae throughout the entire valve. When considering the entire cell cycle, conspecificity is to be excluded based on the variable valve outline in G. maritimo-antarcticum (ranging from linear-lanceolate to rhombic-lanceolate) compared to the typical clavate, broadly lanceolate outline in G. punae and G. pseudoclavatum . Gomphonema punae was described from high elevations (1600–4300 m) in southern Chile, including Patagonia. The new species from Maritime Antarctica is proportionately narrower, being approximately the same width but nearly twice the valve length reported for G. punae . Gomphonema punae is usually shorter (14–26 μm) although no clear difference in valve width could be found, thus it has a more squat valve outline. Other reported (and illustrated) populations always show the same squat valve outline ( Morales et al. 2007, Alvial et al. 2008, Sala et al. 2008) as shown in the type population of G. punae . More elongate valves as could be found in populations of G. maritimo-antarcticum have never been seen in illustrated records of G. punae of South America.

The Antarctic Gomphonema signyense can be separated again by having linear to linear-clavate valves with broader and obtusely rounded headpole, which were not observed in any of the studied populations of G. maritimo-antarcticum , as well as by the comparatively more radiate striae in G. maritimo-antarcticum .