Dreissena elata Andrusov 1897

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).