Monodacna caspia ( Eichwald, 1829 )

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 : 1235

publication ID	https://doi.org/ 10.1016/j.jglr.2019.04.001
DOI	https://doi.org/10.5281/zenodo.5019009
persistent identifier	https://treatment.plazi.org/id/5D36A832-FF92-FFC9-FF37-BF847764FBB4
treatment provided by	Carolina
scientific name	Monodacna caspia ( Eichwald, 1829 )
status	s.l.

Treatment

Monodacna caspia ( Eichwald, 1829) s.l.

( Fig. 4 View Fig : 4, Fig. 7 View Fig : 1).

*1829 C. [orbula] caspia Eichwald : 281, pl. 5, fig. 6.

1986 Monodacna caspia (Eichwald), 1938 – Yakhimovich et al.: 84, pl. 12, fig. 12.

2013 Adacna (Monodacna) caspia caspia ( Eichwald, 1829) – Bogutskaya et al.: 380, fig. 154.

Dimensions – max. L 23.3 mm, H 18.6 mm.

Characterization – The small-sized cardiid shows a variety of shapes and sizes in our Selitrennoye material. The presence of a series of intermediate morphologies ( Fig. 7 View Fig : 1a–d) suggests a single polymorphic species. All specimens have a single cardinal tooth and lack the lateral tooth that typifies Monodacna , yet the thickness and expression of the hinge is extremely variable. Acommon form is thin-shelled, relatively convex with straight posterior margin and relatively well developed, regularly spaced but thin ribs ( Fig. 7 View Fig : 1c). This shape conforms to shells of M. caspia illustrated in Bogutskaya et al. (2013). Another form is flatter, in general slightly thicker shelled and has a distinct wedge-shape ( Fig. 7 View Fig : 1a). Its ribs are lower and slightly more irregular than in the previous form. This wedge-shaped form conforms to several modern Monodacna species as reported in Bogutskaya et al. (2013) such as Monodacna albida ( Logvinenko and Starobogatov, 1967) and M. polymorpha ( Logvinenko and Starobogatov, 1967) that have been tentatively grouped into one species by Wesselingh et al. (2019).

Taxonomic notes – Our findings of a large morphological variation in Monodacna , with typical forms conforming to modern species but also with all kind of intermediates, either shows that (1) we are dealing with an ancestral species of all or most of the present-day Caspian Monodacna species or (2) that several of the present-day species should be regarded as a single species. Acombined morphological-molecular approach is required to assess the species delimitations within living faunas.

Ecology – Caspian Monodacna species occur in a wide range of habitats today, and given the uncertainty of the identity of these species, it is difficult to report the ecological characteristics. Species live mainly in northern CS on muddy and sandy-muddy substrates at a maximum depth of 40 m ( Bogutskaya et al., 2013). Monodacna species are filter feeders whose salinity preferences range mostly from 2 to 8 psu ( Bogutskaya et al., 2013).

Kingdom	Animalia
Phylum	Mollusca
Class	Bivalvia
Order	Veneroida
Family	Cardiidae
Genus	Monodacna