Dreissena elata Andrusov, 1897

van de Velde, Sabrina, Yanina, Tamara A., Neubauer, Thomas A. & Wesselingh, Frank P., 2020, The Late Pleistocene mollusk fauna of Selitrennoye (Astrakhan province, Russia): A natural baseline for endemic Caspian Sea faunas, Journal of Great Lakes Research 46 (5), pp. 1227-1239 : 1237

Dreissena elata Andrusov, 1897

( Fig. 7 : 2, Fig. 8 : 4–5).

*1897 Dreissensia [sic] polymorpha var. elata Andrusov : 353, pl. 20, fig. 25.

2013 Dreissena elata ( Andrusov, 1897) – Bogutskaya et al.: 321, fig. 108.

Dimensions – max. L 9 mm, H 19.4 mm. Logvinenko and Starobogatov (1969) reported Hup to 30 mm.

Characterization – Medium- to thick-shelled triangular-shaped Dreissena with a wide range of morphologies, ranging from an elongated form ( Fig. 8 : 4) to a short form ( Fig. 8 : 5). In general, the valves have a well-developed keel that runs close to the posteroventral margin; the latter is straight or can be concave in its upper half. The initial part of the dorsal margin is flaring and the inflection towards the lower dorsal margin is usually well developed. Adult shells can be somewhat flaring. The overall shell is broad and the lower margin is rounded.

Taxonomic notes – The systematics and taxonomy of this species are not resolved. Dreissena elata has several characteristics in common with the widespread Eurasian D. polymorpha Pallas, 1771 (whose distribution nowadays also includes North America). The Caspian material resembles D. polymorpha , especially with regard to shape of the keel, but it is broader, thicker and somewhat flatter. However, also very slender forms exist together with intermediates in the studied material ( Fig. 7 : 2). Molecular studies would be required to assess whether D. elata and D. polymorpha are conspecific.

Ecology – Before the introduction of Mytilaster minimus , D. elata was abundant in the South and Middle Caspian basins at depths of up to 35 m mainly on firm ground and shelly/stony substrate. By now, it is probably extinct ( Logvinenko and Starobogatov, 1969). The species occurred in salinities between 2 and 8 psu ( Bogutskaya et al., 2013).

Figures

Fig. 7. Plasticity (shape variability) of (1) Monodacna caspia RGM.1309807. (a) umbo in the middle, more square (b) umbo not in middle, more round (c) umbo in the middle, oval (d) umbo not in middle, more oval shape. (2) Dreissena elata. (a) RGM.1310278 short, curved (b) RGM.1310280 medium, curved (c) RGM.1310280 long, curved (d) RGM.1310280 medium, straight (e) RGM.1310282 long, straight. Scale bars = 1 mm.

Fig. 8. Dreissenidae. (1–3) Dreissena caspia Eichwald, 1855: (1a) RGM.1310289 short type, LV; (1b) RGM.1310288 short type, RV; (2a) RGM.1310286 medium/curved type, LV; (2b) RGM.1310287 medium/curved type, RV; (3a) RGM.1310285 elongated type, LV; (3b) RGM.1310284 elongated type, RV. (4–5) Dreissena elata Andrusov, 1897: (4a) RGM.1310283 elongated type, LV; (4b) RGM.1310282 elongated type, RV; (5a) RGM.1310279 short type, LV; (5b) RGM.1310278 short type, RV). (6–7) Dreissena grimmi Andrusov, 1890: (6a) RGM.1310276 straight type, LV; (6b) RGM.1310275 straight type, RV; (7a) RGM.1310274 curved type, LV; (7b) RGM.1310273 curved type, RV. Scale bars = 1 mm.