Hippodonta communis A. Pavlov, Levkov, D. M. Williams & Edlund 2013, sp. nov.
Creators: name: Pavlov, Aleksandar
name: Levkov, Zlatko
name: Williams, David M.
name: Edlund, Mark B.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Chromista
Bacillariophyta
Bacillariophyceae
Naviculales
Naviculaceae
Hippodonta
Hippodonta communis

description: Hippodonta communis A. Pavlov, Levkov, D.M. Williams & Edlund, sp. nov. (Figs 535–543, 555)   
 Type:— RUSSIA. Lake Baikal, Vydira, sediment, 20 m depth, 23 June 1998, collector D.M. Williams. (holotype: slide BM! 100465; isotype: slide MKNDC! 005845/A).   
Valves narrow, rhombic-lanceolate, with acutely rounded valve ends, not protracted. Valve length 19.6–26.6 µm, valve breadth 4.0–5.0 µm. Axial area narrow, linear throughout, rarely observed as broad, expanding into a prominent, panduriform central area. Central area consistently forming fully developed fascia. Terminal area small, clearly distinguishable with LM, lunar-shaped, and cap-like. Raphe linear-filiform, with pronounced teardrop-shaped and distantly positioned central pores. Terminal pores of raphe less pronounced than central pores, vaguely distinguishable with LM, simple linear, weakly advancing into the terminal area. Striae coarse, of variable pattern at middle, weakly to strongly radiate, becoming parallel to weakly convergent towards valve ends, 9–12 in 10 µm. Interstriae of lesser width than striae, equally pronounced throughout. Lineolae composing the striae clearly discernible with LM, large, 3 or 4 along a stria at middle of valve.  
SEM: Externally, valve face flat (Fig. 555). Terminal areas weakly expanding onto valve face. Striae uniseriate. Lineolae prominent and long, but simple linear. Row of areolae positioned on apical valve mantle, also uniseriate. Prominent hyaline area present throughout valve mantle, absent of any structure. Girdle band quite broad and unornamented.  
 Distribution:— Hippodonta communis has so far only been observed in Lake Baikal, Russia. Quite abundant at the type locality.   
 Observations:—With respect to valve outline and striae pattern, H. communis is most similar to H. certa (Figs 526 – 534). Still, H. communis has a lower valve width when valves of equal length are compared, as well as fewer lineolae within a stria at the middle of the valve compared with the number of lineolae in H. certa (4–6 within a stria).   
 Hippodonta acus Kulikovskiy, Metzeltin & Lange-Bert. in Kulikovskiy et al. (2012: 143, figs 67: 13, 14) (Figs 544–546)   
Valves quite narrow-rhombic, with weakly protracted and acutely rounded valve ends. Valve length 24.4–35.4 µm, breadth 3.7–5.3 µm. Axial area narrow linear throughout, expanding into a prominent panduriform central area. Central area consistently forming fully developed fascia. Terminal area prominent, clearly distinguishable with LM, triangular in shape. Raphe linear-filiform, with pronounced teardrop-shaped, closely spaced central pores. Terminal pores of raphe less pronounced than central pores, clearly distinguishable with LM, simple-circular, not advancing into the terminal area. Striae coarse, rarely observed as fine, weakly radiate at middle, becoming parallel towards valve ends, 7–11 in 10 µm. Interstriae of equal or greater width than striae, pronounced stronger towards valve centre. Lineolae composing striae, vaguely discernible with LM, 3 or 4 along a stria at middle of valve.  
 Distribution:— Hippodonta acus has so far only been observed in Lake Baikal, Russia. In the present study this species was found in a 0.8 m deep sand sample, 5 km east from Nizhneangarsk.   
 Observations:— Hippodonta acus has characteristically narrow and acutely rounded valve ends, thus showing a resemblance only to H. acuta (Figs 470–481). Hippodonta acus can be distinguished by the consistent presence of a well-developed panduriform fascia as well as by the more strongly pronounced interstriae throughout the valve length.
description: Published as part of Pavlov, Aleksandar, Levkov, Zlatko, Williams, David M. & Edlund, Mark B., 2013, Observations on Hippodonta (Bacillariophyceae) in selected ancient lakes, pp. 1-53 in Phytotaxa 90 (1) on pages 32-33, DOI: 10.11646/phytotaxa.90.1.1, http://zenodo.org/record/5071976