Hippodonta affinis A. Pavlov, Levkov, D.M. Williams & Edlund, 2013

Pavlov, Aleksandar, Levkov, Zlatko, Williams, David M. & Edlund, Mark B., 2013, Observations on Hippodonta (Bacillariophyceae) in selected ancient lakes, Phytotaxa 90 (1), pp. 1-53 : 18

Hippodonta affinis A. Pavlov, Levkov, D.M. Williams & Edlund , sp. nov. ( Figs 192–200 , 224 )

Type:— MACEDONIA. Lake Prespa , Bay of Konjsko, mud, 2.5 m depth, 25 May 2003, collector Z. Levkov. (Accession No. MKNDC 000537; holotype: slide MKNDC! 000537/1; isotype: slide BM! 101641) .

Valves elliptic-lanceolate, with broad and slightly protracted, acutely rounded valve ends. Valve length 13.0– 18.5 µm, width 5.0–6.0 µm. Axial area linear and moderately broad, expanding into a panduriform central area. Central area forming well-defined fascia, expanding to the valve margins and continuously broadened towards the margins. Terminal area distinguishable in LM view, quite small and semi-circular in shape. Raphe linear-filiform, with clearly pronounced, round and closely spaced central pores. Terminal pores of raphe barely discernible in LM, as simple linear and abruptly terminated. Striae coarse, moderately to strongly radiate at the middle, becoming parallel or weakly convergent towards valve ends. Striae evenly spaced throughout, 10–12 in 10 µm. Interstriae of lower width than striae, evenly pronounced throughout valve length. Lineolae composing striae large and clearly discernible with LM, 4 or 5 within a stria at the middle of the valve.

SEM: Externally, valve face flat ( Fig. 224 ). Terminal area weakly expanding onto valve face. Terminal pores of raphe simple linear, positioned before terminal area. Striae uniseriate, lineolae simple linear, strongly pronounced and long, c. 40 in 10 µm.

Distribution:— Hippodonta affinis has so far only been observed in Lake Prespa, Macedonia, where it occurs in the littoral sediment (2–4 m depth).

Observations:—A specimen illustrated in Lange-Bertalot (2001: fig. 78: 15) from the Albanian part of Lake Prespa and identified as H. rostrata , most likely belongs to H. affinis . The morphology of H. affinis closely resembles H. rostratoides ( Figs 180–191 ) and H. media ( Figs 156–165 ), both from Lake Prespa. Nevertheless, H. rostratoides has longer and narrower protracted valve ends, whereas the valve ends of H. media are not protracted, compared to the broadly and short protracted valve ends in H. affinis .

A specimen depicted in Tuji (2003: fig. 8: 28) from Lake Biwa, Japan, resembles H. affinis with regard to the valve outline and the appearance of the striae. Still, the valve ends of H. affinis are clearly more protracted and the striation being finer as well. The name H. subcostulata is incorrectly given for the specimen illustrated by Tuji (2003: fig. 8: 28). However, it may belong to Navicula costulata var. nipponica Skvortsov (1936: 272 , fig. 5: 12) described from Lake Biwa.

Figures

FIGURES 166–218: LM micrographs. Figs 166–179. Hippodonta subrostrata (type material). Figs 180–191. Hippodonta rostratoides (type material). Figs 192–200. Hippodonta affinis (type material). Figs 201–212. Hippodonta exigua (type material). Figs 213–218. Hippodonta humboldtiana (type material). Scale bar = 10 µm.

FIGURES 219–225: SEM micrographs. Figs 219–222. Hippodonta abunda (type material). Fig. 219. External view of entire valve. Terminal pores of raphe are simple linear depressions. Fig. 220. External view of complete frustule showing broad, unornamented girdle. Fig. 221. Internal view of entire valve. Striae positioned in shallow depressions, helictoglossae in line with raphe slits. Fig. 222. Close-up of one half of valve, internal view. Lineolae covered by quite prominent elliptical volae. Fig. 223. Hippodonta rostratoides (type material). External view of entire valve. Lineolae quite prominent. Terminal pores of raphe slightly deflected towards one valve side. Fig. 224. Hippodonta affinis (type material). External view of entire valve. Lineolae narrow but long. Terminal pores of raphe simple linear. Fig. 225. Hippodonta exigua (type material). External view of entire valve. Lineolae weakly pronounced, short. Terminal pores of raphe slightly deflected towards one valve side. Scale bars in Figs 219, 223, 224 = 5 µm; Fig. 220 = 2 µm; Fig. 221 = 6 µm; Fig. 222 = 3 µm; Fig. 225 = 4 µm.

FIGURES 102–165: LM micrographs. Figs 102–137. Hippodonta abunda (type material). Figs 138–155. Hippodonta microcostulata. Figs 156–165. Hippodonta media (type material). Scale bar = 10 µm.