Psammothidium alpinum 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 : 53

Psammothidium alpinum Potapova & Enache sp. nov. ( Figs 9–21 , 40–44 )

Valvae linearae ellipticae, ovalis, 6.3–9.1 µm latae, 14.6–30 µm longae. Raphovalva cum area axialis angusta linearis versus, area centralis rectagularis. Raphe recta poris centralibus unciformis, termini distale punctiformis. Araphovalva cum area axialis angusta, area centralis circularis, irregularis, 1/2 valvae lata. Striae transapicales paulo radiatae, 22–25 in 10 µm cum striae breviores intercalares. Areolae rotundae, grossae, 25 in 10 µm.

Valves linear-elliptic to oval, 6.3–9.1 µm wide, 14.6–30 µm long. Raphe valve with narrow linear axial area and rectangular-irregular central area. Raphe straight with hook-like proximal pores, drop-shaped distal endings ( Figs 10, 11, 13, 15, 16, 20 ). Rapheless valve with narrow axial area, irregular, rounded central area, occupying about ½ of valve breadth ( Figs 9, 12, 14, 17–19, 21 ). Transapical striae slightly radiate, 22–25 in 10 µm, with shortened marginal striae present (figs 41, 43). Areolae coarse, round, 25 in 10 µm ( Fig. 44 ).

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 9, 10 ) on slide GC64862 , accession # GC64862 ( ANSP!), holotype, designated here; circled specimens on slide GC64863 ( ANSP!) and slide 84223 ( CANA!), isotypes, designated here) .

Etymology: —specific epithet refers to the occurrence of the new species in alpine, high elevation lakes.

Psammothidium alpinum is similar to P. bioretii ( Germain 1957: 85) Bukhtiyarova et Round (1996: 9) in valve size and possession of relatively coarse areolae. It differs from P. bioretii by having more elongate, linear-elliptical valve shape with nearly parallel sides, and a straight central sternum (versus diagonal in P. bioretii ). In SEM ( Figs 40–44 ), P. alpinum displays a characteristic doublet of smaller areolae at the valve/ mantle junction and around the mantle ( Figs 40, 42 ). On raphe valves, the central area nearly reaches the valve margin and is bounded by 4–8 short striae. The raphe has characteristic hook-like widely spaced proximal endings ( Fig 40 ) that deflect in the same direction externally ( Fig. 40 ) and opposite internally ( Fig. 41 ). While P. bioretii has terminal raphe fissures curved to opposite sides, P. alpinum lacks terminal fissures, and distal external raphe endings are drop-shaped and do not expand beyond the last stria ( Fig. 41 ). Similar to P. bioretii , P. alpinum has coarse, round areolae visible in LM; a row of coarser areolae border the sternum and central area in LM ( Figs 10, 11 ) and a double row of finer areolae bordering the valve face-mantle junction is visible in SEM ( Figs 40, 42 ). Short intercalary striae are present along the valve margin and expand on the mantle ( Figs 41, 43 ). Psammothidium alpinum has similar valve shape as P. chlidanos ( Hohn et Hellerman 1963: 273) Lange-Bertalot (1999: 285) but it can be easily distinguished by its coarser striae and areolae visible in LM.

P. alpinum was present in Hidden Lake NOCA (bottom sample, 2% relative abundance) and very rare in top samples from Snow and Stiletto lakes.

Figures

FIGURES 1–21: LM micrographs of Psammothidium species from Snow Lake, Washington Cascades. Figs 1–8. Psammothidium lacustre sp. nov. Figs 1–2. Holotype specimen, slide ANSP GC64860. Figs 9–21. Psammothidium alpinum sp. nov. Figs 9–10. Holotype specimen, slide ANSP GC64862. Scale bar = 10 µm.

FIGURES 40–44: Psammothidium alpinum sp. nov., SEM. Figs 40–42. Type material, Snow Lake, sample ANSP WACA019 Fig. 40. External view of raphe valve. Fig. 41. Internal view of raphe valve. Fig. 42. External view of rapheless valve. Fig. 43. Internal view of rapheless valve, Hidden Lake NOCA, sample ANSP WACA018. Fig. 44. Areolae on the internal surface of the valve, Snow Lake, sample ANSP WACA001. Scale bars = 1 µm.