Planothidium piipii Tseplik, Glushchenko, Maltsev et Kulikovskiy 2024, sp. nov.

Planothidium piipii Tseplik, Glushchenko, Maltsev et Kulikovskiy sp. nov. (Figs. 2–105) Holotype. Slide no. kam197, in the collection of Maxim Kulikovskiy, Institute of Plant Physiology, Russian Academy of Sciences, Russia, represented here by Figure 3. Reference strain. kam197 (08029), isolated from sample 44. Type locality. Russia, Pushchinskiye mineral springs, sample 44, scrapes from stones(N 54.01.616, E 158.040.972), 11.07.2021. Description. LM (2–93). Valves lanceolate or rhombic-lanceolate, slightly asymmetric, with protracted to slightly subcapitate ends; smaller valves are elliptic or elliptic-lanceolate to roundish, with broadly rounded ends. Length 5.0– 23.0 μm, width 4.0–7.0 μm. Raphe straight, filiform, distal ends bent to one side. Axial area on the raphe valve narrow, linear. Central area asymmetrical or roundish, formed by several striae being shortened on one or both sides. Striae radiate, 13–19 in 10 μm. Axial area on the rapheless valve narrow, linear to linear-lanceolate. A large sinus is present on one side of the valve; on the opposite side, several striae are shortened, forming a small semicircular central area. Striae weakly radiate, 13–18 in 10 μm. SEM (94–105). External central raphe ends straight, expanded, distal ends bent to one side. Internal central raphe ends slightly turned in opposite directions, distal ends terminate in faint helictoglossae. Axial area on the rapheless valve is ornamented with small circular depressions that are most concentrated on the central part of the valve. A vestigial raphe may be seen on the internal side of the rapheless valve. Striae multiseriate, composed of 2–4 rows of areolae on the raphe valve and 2–3 rows on the rapheless valve. Areolae small, round. Internally, the interstriae are distinctly raised. Sequence data. Partial 18S rDNA gene sequence comprising V4 domain sequences (GenBank accession number PQ066498 for the strain kam197, PQ066499 for the strain kam233, PQ066500 for the strain kam277, PQ066502 for the strain kam303, PQ066503 for the strain kam316, PQ066504 for the strain kam407) and partial rbc L sequences (GenBank accession number PQ074208for the strain kam197, PQ074209 for the strain kam233, PQ074210 for the strain kam277, PQ074212 for the strain kam303, PQ074213 for the strain kam316, PQ074214 for the strain kam407). Etymology. The species is named in honour of Boris Ivanovich Piip (1906–1966), a renowned Russian geologist, petrographer, and volcanologist who dedicated his research to the study of volcanoes, thermal springs, and the geological structure of Kamchatka. He was the founder and first director of the Volcanology Institute at the Siberian Branch of the Academy of Sciences of the USSR, and under his leadership, the activities of the Kamchatka Branch of the Geographical Society were revived. Ecology. This species was isolated from several freshwater water bodies, including a mineral creek, from samples of benthos and epiphytes. Distribution. As yet known only from the type locality.