Adlafia ossiformis Alibert & Hamilton & Pienitz & Antoniades 2023, sp. nov.

Adlafia ossiformis sp. nov. (Figs 10 AH-AT; 13 A-H)

HOLOTYPE. — Canada. Québec, Lake 22AA, 56°33’24”N, 76°28’47”W, 128 m a.s.l., 22.VIII.2015, D. Antoniades (microscope slide designated as the holotype, holo-, CANA [CANA 129481]).

ISOTYPE. — Canada. Québec, Lake 22AA, 56°33’24”N, 76°28’47”W, 128 m a.s.l., 22.VIII.2015, D. Antoniades (iso-, ANSP [ANSP-GC68069]).

TYPE LOCALITY. — Canada. Québec, Lake 22AA, 56°33’24”N, 76°28’47”W, 128 m a.s.l.

ETYMOLOGY. — The epithet ‘ossiformis’ is Latin, describing this species’ bone-shaped valves.

ECOLOGY AND DISTRIBUTION. — This species was found only in 22-AA lake of the study, where it represented 4% of the diatom assemblage. Lake 22-AA had the highest TP concentration in the dataset (23.4 µg/L).

REGISTRATION. — http://phycobank.org/103920.

Frustules rectangular and narrow in girdle view.Valves elliptic at mid-valve with broad capitate ends. Valve dimensions (n =20): length 13.5-20.5 µm, width 4.5-5.5 µm and 30-35 striae in 10 µm. External valve face flat, margin rounded. Axial area slightly curved to linear and narrow. Central area round to elliptic,>1/2 width of valve, with 5-7 marginal striae between proximal raphe endings. Raphe linear, with no kink-like irregularity halfway between mid-valve and apex (Fig. 13A); externally, central raphe fissures widely spaced with small indistinct ends bent to one side (Fig. 13C). Terminal raphe fissures curved down onto upper region of mantle (Fig. 13G). A weakly formed groove present parallel to raphe on mantle up to valve face. Internally, raphe on small sternum, straight, with no kink-like irregularity (Fig. 13B). Proximal raphe fissures bent and deflected on a raised nodule (Fig. 13D). One surface depression present on central nodule (Fig. 13D, E). Terminal fissures end on small elongated helictoglossae, isolated from apex mantle (Fig. 13H). Hyaline area of terminal nodule more developed on secondary side of valve. Striae continuous, straight to weakly arched from valve face to mantle, more widely spaced around central area. Voigt faults weak to indistinct on secondary side of valve 2/3 of distance between mid-valve and apex. Striae continuous around base of apices. Areolae round to rectangular, 4-6 per stria. Areolae covered with a fine poroid velum with 8-9 circular rows of small pores around outside edge and linear rows on inner area. Internally, areolae recessed between virgae.

Adlafia ossiformis sp. nov. has a shape that is easily confused in LM with Psammothidium ventralis (Krasske) Bukhtiyarova & Round and Sellaphora guyanensis Metzeltin & Lange-Bertalot, but careful examination of both valves will make species differentiation possible.