Cavinula vincentii Antoniades & Hamilton

Cavinula vincentii Antoniades & Hamilton (Figs 74–81, 172–180)

Valves elliptic with broadly rounded ends. Valve length 11–13.5 µm, width 8–10 µm. Striae radiate at center, more strongly radiate towards ends, 22–26 in 10 µm. Striae uniseriate with elliptical to rounded areolae discernable in LM. Axial area narrow, linear; central area small, elliptical or almost round, to asymmetrically elongated. Short and long alternating striae surround the central area. Short striae along valve length, extend onto valve mantle. Internally striae between thickened costae and areolae covered with a hymen. Externally, raphe filiform. Proximal raphe fissures expanded pores, slightly unilaterally bent; distal raphe fissures small pores, terminating on valve face. Internally, raphe linear, positioned on thickened sternum. Terminal raphe fissures with a helictoglossa, not present on proximal raphe ends. Adjacent to distal raphe ends one enlarged, transversally elongated pore-like fissure, externally separated with a small ridge-like structure from areolae. Copulae open bands, with one row of pores, two or more at each valve.

Type: –– White Pond, Alert, Ellesmere Island, Nunavut, Canada. Antoniades et al. 2009, figs 7–9 (holotype). Here presented in Figs 172–180 (type material).

Observations:— Cavinula vincentii was described from Ellesmere Island, Canada. The taxon resembles the elliptical forms of C. pseudoscutiformis (Figs 44–53), but it is clearly distinguished by the valve outline, which is more elliptical, has a larger central area and the general morphology of the raphe. The main morphological character which separates C. vincentii from C. pseudoscutiformis and also the other taxa belonging to the genus Cavinula is the presence of the pore-like fissures at the valve apices. Based on SEM photomicrographs one other taxon, C. scutiformis has distinct pore-like fissures at the valve apices. Additionally, a specimen identified by (Krammer & Lange-Bertalot, 1986, fig. 59: 12) as C. pseudoscutiformis from Europe appears to be similar to C. vincentii, but a more detailed LM and SEM observation is necessary to confirm this.

Distribution:— Antoniades et al. (2009) described C. vincentii from the locality White Pond, Alert, Ellesmere Island, Nunavut, a shallow pond with inorganic sediments and high pH (8.3). During our observation of a number of slides deposited at the CANA Diatom Collection, the presence of C. vincentii was confirmed in the following localities: two sediment cores recovered from the deepest part of Lake Oakley and Little Clear Lake, respectively, both lakes located in the province of Ontario. This taxon was also observed in the recent samples from Lake Abitibi (Québec), Lake Contwoyto (Northwest Territories) and in samples originating from Isachsen (Ellef Ringnes Island, Nunavut Territory). Additionally, C. vincentii was confirmed from one samples collected in Pennsylvania (Fig. 77). This taxon is present in mildly acidic to circumneutral, oligotrophic waters across northern North America.

Distribution Records:— Antoniades et al. (2009, figs 7–9, 12, 13, 60–64, Arctic Archipelago).