Didacna subcatillus Andrussov 1910
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 subcatillus

description: Didacna subcatillus Andrusov, 1910
(Fig. 5: 3, Fig 6: 1-3).
*1910 Didacna catillus var. subcatillus Andrusov: 78, pl. 9, figs. 22–23.
1953 Didacna subcatillus Andrussov – Fedorov: 127, pl. 14, figs. 16–20.
1958 Didacna subcatillus Andrussov – Nevesskaja: 24, pl. 3, figs. 1–6.
1986 Didacna subcatillus Andrussov, 1910 – Yakhimovich et al.: 84, pl. 4, figs. 3, 4.
2007 Didacna subcatillus subcatillus Andrussoff, 1910 – Nevesskaja: 935, pl. 21, figs. 6–14.
Dimensions – max. L 43.4 mm, H 33.8 mm.
Characterization – Didacna subcatillus is a broad trapezoid highly variable species that does harbor several specific forms that we could link through intermediates forms in the studied material (Fig. 6: 1–3). The posterodorsal keel is usually low, the posterior margin is rounded. The posterior ridge is pronounced and mostly angular in juvenile stages and can become more subrounded in adult stages. The posterior ribs range between 18 and 25. Interspaces are narrow (about 40–60% of the width of the ribs). Towards the anterior margin ribs become often less pronounced and the posterior rib width and prominence increases towards the posterodorsal ridge. The rib cross-section is irregular, usually flat or subrounded. The location of the semidiameter is on the posterior ridge in juveniles and close to the center of the shell in adults. The ventral half of the shell is typically straight and dipping. Juvenile shells have already a trapezoid to low trigonate outline with a barely rounded lower margin and a well-developed posterodorsal keel. We found strong variations in shell shapes and sizes and investigated the possible presence of sibling (sub-)species. Some individuals grow as large as 43.4 mm (L) × 33.8 mm (H), while 95% of individuals show maximum dimensions of 15 mm (L) × 12 mm (H). One particular phenotype is small, has a thick shell that is somewhat convex and has markedly thick hinge plate and teeth and regularly developed ribs that have a more or less rounded cross-section (Fig. 6: 1a, 2a). This form however is connected via intermediates (Fig. 6: 1b, 1c, 2b, 2c) with thin-shelled forms that are less convex and have thinner hinge features (Fig. 6: 1d, 2d).
Taxonomic notes – The various forms of Didacna subcatillus have been attributed to a number of species and forms in the past, to which Nevesskaja (2007) attributed biostratigraphic value. However, we were unable to delimit these forms in our variable material (Fig. 8) and consider them synonyms.
Ecology – Unknown (extinct). Didacna subcatillus preferred lower saline waters than most Didacna species (Nevesskaja, 1958; Yanina, 2012).
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 1233-1234, DOI: 10.1016/j.jglr.2019.04.001, http://zenodo.org/record/5019200