Petroplacus lizae Pomazkina, Rodionova, Sherbakova & D.M.Williams, 2016

Pomazkina, Galina, Rodionova, Yelena, Sherbakova, Tatyana & Williams, David. M., 2016, Petroplacus gen. nov. (Bacillariophyta): a new genus of diatom from Lake Baikal, Phytotaxa 272 (4), pp. 267-276 : 269-270

Petroplacus lizae Pomazkina, Rodionova, Sherbakova & D.M.Williams , sp. nov. ( Figs 1–22 )

LM: Valves linear-elliptic to linear broad with protracted rostrate ends, 25–35 μm long, 15–18 μm wide. Axial area linear, widening towards valve centre forming a transversely elongated central area. Raphe straight, external central raphe endings expanded into T-shaped grooves. Transapical striae radiate, 13–16 in 10 μm at valve centre, 17–22 in 10 μm at apices; irregular shorter striae at valve edge between main striae. SEM: Valves flat, linear-elliptic to broadly linear, with shallow mantle. Striae composed of small round densely disposed poroids, 35–50 in 10 μm. Externally, central raphe endings expanded into deep T-shaped grooves, terminal fissures deflected bluntly to secondary side. Internally, central raphe endings straight, filiform, with pronounced central nodule. Distal raphe endings terminate in simple helictoglossae, slightly bent away from centre. Areolae openings occluded by simple volae, which coalesce with neighboring volae to form a chain-like structure within a stria. Cingulum composed of two slit narrow bands regularly perforated by fine pores.

Type:— RUSSIA. Lake Baikal: Northern basin, Cape Elokhin , sand sample collected by diver in the littoral zone at st. 12, 29 June 1997 (holotype: slide 0043-BK housed at the Limnological Institute SB RAS, Irkutsk, Russia, here illustrated as Fig. 1 . Isotypes: BK! slide 0043 (st. 12), Limnological Institute SB RAS, Irkutsk, Russia; BM! 100353) .

Etymology:— The specific epithet is named after Liza Clark, the grandchild of the author G. Pomazkina. Distribution:— Known only from the type locality.

Figures

FIGURES 1–12. Light micrographs. 1−12. Petroplacus lizae. LM views showing variations in size and valve outline. Fig. 1 is the holotype. Scale bar = 10 μm.

FIGURES 13–22. Scanning electron micrographs. Petroplacus lizae from type material. 13−16. SEM external views of entire valve showing raphe and striae structure. 14. SEM external detail of valve centre with proximal raphe endings expanded into T-shaped grooves, uniseriate striae. 15, 16. SEM external detail of valve apex with terminal fissures. 19–22. SEM views of entire valve showing raphe and striae structure. 20. SEM internal detail of valve centre with proximal raphe endings, volate occlusions of the areolae. 21. SEM internal detail of valve apex with helictoglossa, round pores occluded by volae. 22. SEM internal detail of broken valve showing the pores apertures. 17. SEM detail of girdle band with a single row of pores. 18. SEM detail of two girdle bands. Scale bars = 10 μm (Figs 13, 19), 3 μm (Figs 14, 20, 21), 5 μm (Figs 17–18), 2 μm (Fig.22), 1 μm (Figs 15–16).