Dreissena elata Andrusov, 1897

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

1969 Dreissena elata (Andr.). - Logvinenko and Starobogatov: 316, fig. 341(1).

1994 Dreissena elata Andrusov, 1897. - Rosenberg and Ludyanskiy: 1482, fig. 3g.

2013 Dreissena elata (Andrusov, 1897). - Kijashko in Bogutskaya et al.: fig. 108.

2016 Dreissena (Dreissena) elata (Andrusov, 1897). - Vinarski and Kantor: 76.

Status. Pontocaspian species, endemic to the Caspian Sea, probably extinct. Species status uncertain.

Type locality. Kuuli Cape, Dazmyk, Apsheron Peninsula, Azerbaijan (Vinarski and Kantor 2016).

Distribution . Caspian Sea. Probably extinct.

Taxonomic notes. Dreissena elata has morphological features in common with D. polymorpha, including a relatively wide shell and a well-pronounced keel located close to the ventral margin. However, the D. elata shell is in general wider, flatter, and has a more rounded abapical margin even though shell characters are higly variable. Dreissena elata has been reported from areas in the Caspian Sea with salinities well above 5 ‰, which is unusual for D. polymorpha elsewhere. We are uncertain whether D. elata might be a sibling species. Its apparently distinct morphology and autecological preferences suggest it is different from D. polymorpha, but it will require molecular comparison to investigate whether it concerns a mere morph that has undergone "ecological release" (Kohn 1972) or is a different species. However, no living specimens of D. elata have been recorded since 1957 (Kostianoy and Kosarev 2005) when its Caspian habitats were invaded by Mytilaster minimus .

Conservation status. Not assessed. It was reported as extinct by Kostianoy and Kosarev (2005, and references therein). If D. elata is accepted as a valid species, it might qualify for the same conservation status as D. caspia (critically endangered, possibly extinct; von Rintelen and Van Damme 2011b).