Didacna cristata Bogachev 1932
Creators: name: van de Velde, Sabrina
name: Yanina, Tamara A.
name: Neubauer, Thomas A.
name: Wesselingh, Frank P.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Bivalvia
Veneroida
Cardiidae
Didacna
Didacna cristata

description: Didacna cristata Bogachev, 1932
(Fig. 5: 6).
*1932 Didacna praetrigonoides var. cristata Bogachev: 44, pl. 4, figs. 9–14.
1948 Didacna cristata Bogachev – Fedorov: 19, pl. 1, figs. 4–6, pl. 2, figs. 4–8.
1953 Didacna cristata Bogachev – Fedorov: 127, pl. 16, figs. 1– 11.
1983 Didacna cristata Bogachev, 1932 – Popov: 201, pl. 12, figs. 9–22.
Dimensions – max. L 19.8 mm, H 16.3 mm.
Characterization – Medium-sized, relatively high, subtrigonate to subovate convex and robust Didacna. Beak clearly defined. Posterodorsal margin steep, thin, well delimited. Semidiameter located on posterior ridge that is well developed and sharp. In about half of the specimens two elevated ribs form the posterior ridge. Posterior margin rounded angular. Between 15 and 21 posterior ribs that are wide and flat and about three times as wide as the interspaces. Juveniles have a wide trapezoid outline with a rounded lower margin and a subtruncate posterior margin. The hinge plate and cardinal teeth are robust.
Taxonomic notes – Bogachev (1932) distinguished the new variety D. praetrigonoides var. cristata from typical D. praetrigonoides by its smaller size, more triangular outline and sharper keel. Fedorov (1953) showed that the variety not only differs in shape and size from D. praetrigonoides but also in its stratigraphic position. While D. praetrigonoides is characteristic for the upper Khvalynian deposits, D. praetrigonoides var. cristata is an index fossil of the lower Khvalynian of the east coast of the Caspian Sea. Fedorov (1953) mentioned that the juvenile D. praetrigonoides forms are similar to D. cristata. Nevesskaja (1958) disagreed with Fedorov while studying a collection of mollusks from the Khvalynian deposits of West Turkmenistan. She stated that the Khvalynian beds of Turkmenistan yielded relatively small shells (up to 50 mm long), with a well-developed plate like a keel and a small number of ribs (23–27). Nevesskaja (1958) concluded that the variety should not be regarded as a distinct taxon because it only shows the plasticity of the species but cannot be well delineated in time or space (see also Nevesskaja, 2007). In contrast, Popov (1983) supported the opinion of Fedorov (1953) based on a comparative statistical analysis of shell dimensions of D. cristata and D. praetrigonoides (Table 41 in Popov, 1983). He demonstrated that the differences between D. cristata and D. praetrigonides were bigger than between many others Quaternary Didacna species. Here, we follow the view of Fedorov (1953) and Popov (1983).
Ecology – Unknown (extinct). In general trigonoid Didacna species prefer low salinities (Yanina, 2012), but since D. cristata is extinct the paleosalinities can only be inferred.
description: Published as part of 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, pp. 1227-1239 in Journal of Great Lakes Research 46 (5) on pages 1231-1232, DOI: 10.1016/j.jglr.2019.04.001, http://zenodo.org/record/5019200