Psammothidium nivale Potapova & Enache, 2013

Enache, Mihaela D., Potapova, Marina, Sheibley, Rich & Moran, Patrick, 2013, Three new Psammothidium species from lakes of Olympic and Cascade Mountains in Washington State, USA, Phytotaxa 127 (1), pp. 49-57 : 54

Psammothidium nivale Potapova & Enache sp. nov. ( Figs 22–31 , 45–48 )

Valvae ellipticae, 5.6–6 µm latae, 11.7–15 µm longae. Raphovalva cum area axialis linearis, area centralis transapicalem rectagularis vel ovalis, 2/3 valvae lata. Raphe recta cum poris proximales paene expansae, in sulci, cum terminis distales simplices. Araphovalva cum area axialis ad apicem angusta, versus centro expansa, rhombico-lanceolata, 2/3 valvae lata. Striae transapicales paulo radiatae, 26–28 in 10 µm in araphovalva, 30–32 in 10 µm in raphovalva.

Valves elliptical, 5.6–6 µm wide and 11.7–15 µm long. Raphe valve with linear axial area, central area transapically rectangular to oval occupying 2/3 of the valve breadth. Raphe with proximal pores slightly expanded, located in grooves, and with simple distal endings ( Figs 23, 25, 27, 28 ). Rapheless valve with axial area narrow at apices and widening towards valve centre in a rhombic-lanceolate shape, occupying 2/3 of the valve breadth ( Figs 22, 24, 26, 29, 30 ). Striae slightly radiate, 26–28 in 10 µm on rapheless valve, 30–32 on raphe valve.

Type:— USA. Washington: Cascade Mountains, Snow Lake , 46.7576° N, 121.6982468° W, lake sediment (2–2.5-cm depth core interval; lake maximum depth 9.75 m), collected 07 October 2009, collection WACA019 , (Circled specimen ( Figs 22, 23 ) on slide GC64864 , accession # GC64864 ( ANSP!), holotype, designated here; circled specimens on slide GC64865 ( ANSP!) and slide 84224 ( CANA!), isotypes, designated here) .

Etymology:—specific epithet refers to the name of the lake (Snow Lake) from where the species was found and described.

Psammothidium nivale is distinguished from other Psammothidium species by characteristic coarser striae and areolae on rapheless valve compared to raphe valve. The linear axial area on raphe valves widens slightly near the valve center, and the transapically rectangular to oval central area is bounded by 4–5 shortened striae. External proximal raphe endings are located in grooves, which gradually widen toward valve center. External distal raphe endings are drop-shaped and do not extend beyond the last stria ( Fig. 45 ). Characteristic coarse areolae on rapheless valves have the appearance of transapically elongated slits in SEM ( Figs 47–48 ).

In the SEM, the shape of the areolae—transapically elongate—resemble those of P. subatomoides in SEM. However, P. nivale is distinguished from the latter species by all other valve characteristics: more elongated shape of the valve and larger size, shape of central area on both raphe and rapheless valve and clear dimorphism of raphe and rapheless valve in striae density and areolae size. P.nivale was found in Snow Lake and Hidden Lake NOCA in very low abundance (<0.25% relative abundance).

Figures

FIGURES 22–34: LM micrographs of Psammothidium species from Snow Lake, Washington Cascades. Figs 22–31. Psammothidium nivale sp. nov. Figs 22–23. Holotype specimen, slide ANSP GC64684. Figs 32–34. Psammothidium helveticum. Scale bar = 10 µm.

FIGURES 45–48: Psammothidium nivale sp. nov., SEM. Figs 45–47. Type material, sample ANSP WACA019, Snow Lake. Fig. 45. External view of raphe valve. Fig. 46. Internal view of raphe valve. Fig. 47. External view of rapheless valve. Fig. 48. External view of rapheless valve, Hidden Lake NOCA, sample ANSP WACA018. Scale bars = 1 µm.