Didacna protracta

Wesselingh, Frank, Poorten, Jan Johan ter, Kijashko, Pavel, Albrecht, Christian, Anistratenko, Olga Yu, Frolov, Pavel, Gándara, Alberto Martinez, Gittenberger, Arjan, Gogaladze, Aleksandre, Mikhail Karpinsky, Popa, Luis, Sands, Arthur F, Vandendorpe, Justine & Wilke, Thomas, 2019, Mollusc species from the Pontocaspian region - an expert opinion list, ZooKeys 827, pp. 31-124 : 45-46

Didacna protracta (Eichwald, 1841)

*1841 Adacna protracta Eichwald: 280, pl. 40, figs 10, 11 [non figs 9, 10 as indicated in the text].

1877 Cardium catillus Eichw. - Grimm: 58, pl. 8, figs 7, 8 [non Monodacna catillus Eichwald, 1841].

1910 Didacna protracta (Eichwald, 1841). - Andrusov: 67, pl. 8, figs 22, 33, pl. 9, figs 1-9.

1952 Didacna protracta (Eichwald, 1841). - Zhadin: 348-349, fig. 324.

1953 Didacna protracta (Eichwald, 1829). - Fedorov: 127, pl. 14, figs 12-15, pl. 15, figs 1-16.

1967 Didacna protracta Eichwald, 1841. - Svitoch: 42-43, pl. 6, figs 6-9, pl. 7, figs 1, 2.

1969 Didacna protracta protracta (Eichw.). - Logvinenko and Starobogatov: 327, fig. 347.

1973 Didacna protracta protracta Eichwald, 1841. - Grossu: 133, text fig. 11.

1973 Didacna protracta submedia Andrusov, 1911. - Grossu: 133-134, text fig. 12.

1999 Didacna protracta (Eichwald, 1829). - Fedorov: pl. 12, figs 4-7.

2005 Didacna protracta (Eichwald, 1829). - Yanina: 238-239, pl. 12, figs 9-19.

2007 Didacna protracta protracta (Eichwald, 1829). - Nevesskaja: 938-939, pl. 22, figs 4-13.

2013 Didacna protracta (Eichwald, 1829). - Kijashko in Bogutskaya et al.: 356, fig. 141.

2013 Didacna protracta submedia Andrusov, 1910. - Kijashko in Bogutskaya et al.: 356, fig. 142.

2016 Didacna protracta (Eichwald, 1841). - Vinarski and Kantor: 72.

Status. Pontocaspian species, endemic to Caspian Sea.

Type locality. The type series (?Recent, Caspian Sea) was reported as lost by Nevesskaja (2007) who introduced a neotype from the Elton Lake surroundings in the northern Caspian plains, Russia (early Khvalynian, Late Pleistocene).

Distribution. Middle and southern Caspian Sea basins; it is most common in the middle basin at 25-85 m water depth ( Logvinenko and Starobogatov 1969).

Taxonomic notes. According to Logvinenko and Starobogatov (1969), two subspecies occur in the Caspian Sea at different depth ranges: D. protracta protracta at 25-50 m and D. protracta submedia Andrusov, 1910 at 50-85 m. The latter differs from D. p. protracta by the relative posterior location of the umbo that is furthermore subdued. Both forms of Didacna protracta are widespread in the Khvalynian deposits of the Caspian Sea and Manych depression. According to Kijashko in Bogutskaya et al. (2013) morphological differences characteristic for the subspecies of Didacna protracta are due to allometric growth. The mere difference in depth distribution, with overlapping depths and intermediate forms, does not provide any argument to maintain these subspecies. Didacna protracta is the type species of the subgenus Protodidacna Logvinenko & Starobogatov, 1966.

Remarks. The authorship attribution of this species to Eichwald (1829) as proposed by several authors was rejected in Vinarski and Kantor (2016). According to them, Cardium protractum Eichwald, 1829, described from the western Ukraine, probably refers to a different species.

Conservation status. Not assessed.