Psammothidium lacustre Enache & Potapova & Sheibley & Moran 2013, sp. nov.
Creators: name: Enache, Mihaela D.
name: Potapova, Marina
name: Sheibley, Rich
name: Moran, Patrick
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Chromista
Bacillariophyta
Bacillariophyceae
Achnanthales
Achnanthidiaceae
Psammothidium
Psammothidium lacustre

description: Psammothidium lacustre Enache & Potapova sp. nov. (Figs 1–8, 35–39)
Valvae lanceolate, 8.4–11.2 µm latae, 16.7–28 µm longae. Raphovalva cum area axialis linearis versus centro expanso, area centralis rectangularis, ½ vel 2/3 valvae lata. Raphe recta poris centralibus simples cum cristae et sulci, interne paulo curvatae. Fissuris terminalibus simplex, longae, ad versum curvatae. Araphovalva cum area axialis angusta, area centralis circulare, 2/3 valvae lata. Striae transapicales radiatae 22–26 in 10 µm; areolae cum foramina externae circulares, foramina internae transapicalem elongatae, 40–60 in 10 µm.
Valves lanceolate, 8.4–11.2 µm wide, 16.7–28 µm long. Raphe valve with linear axial area, rectangular central area, occupying ½ to 2/3 of valve breadth (Figs 2, 3, 6, 7). Proximal raphe endings slightly deflected internally (Fig. 36). Terminal raphe fissures simple, long, deflected in opposite directions (Figs 2, 3, 6). Rapheless valve with narrow axial area, round central area occupying 2/3 of the valve breadth (Figs 1, 4, 5, 8). Striae radiate, 22–26 in 10 µm; areolae 40–60 in 10 µm, with round external foramina, and internal openings elongated transapically on both valves (Figs 35–39).
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 1, 2) on slide GC64860, accession # GC64860 (ANSP!), holotype, designated here; circled specimens on slide GC64861 (ANSP!) and slide 84222 (CANA!), isotypes, designated here).
Etymology:—specific epithet refers to the occurrence of the new species in a lacustrine environment.
The species with the closest morphological features to Psammothidium lacustre is P. helveticum (Figs 32– 34). Psammothidium lacustre has much larger size, with valve width greather than 8 µm, and more acute valve ends compared to P. helveticum. SEM investigations (Figs 35–39) revealed that the proximal raphe endings are internally slightly deflected in opposite directions (Fig. 36), similarly to P. helveticum (see Bukhtiyarova & Round 1996, figure 23). The striae extend uninterrupted onto the mantle, and short striae are present near the central area and occasionally in other parts of valve margin (Fig. 38). Areolae have round external foramina and transapically elongated internal openings (Figs 37, 39).
The shape of the axial and central areas on rapheless valves is similar in Psammothidium lacustre and P. helveticum, except that the central area is narrower in P. helveticum. Internally, the shape of areolae is also different: elongated with rims and grooves in P. lacustre versus round or rectangular in P. helveticum (see Bukhtiyarova & Round 1996, figure 23). In LM, P. lacustre is relatively easy to separate from P. helveticum; P. lacustre is larger, has more lanceolate shape, and coarser striae (22–24 versus 23–28) and areolae. Psammothidium lacustre was rare in study lakes (<1% relative abundance).
description: Published as part of 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, pp. 49-57 in Phytotaxa 127 (1) on pages 51-53, DOI: 10.11646/phytotaxa.127.1.8, http://zenodo.org/record/5085461