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Didacna eichwaldi

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Didacna eichwaldi
Shell from the Holocene deposits of the Caspian Sea (Dagestan, Russia)
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Cardiida
Family: Cardiidae
Genus: Didacna
Species:
D. eichwaldi
Binomial name
Didacna eichwaldi
(Krynicki, 1837)
Synonyms
  • Cardium crassum Eichwald, 1829
  • Didacna pseudoprotracta Livental, 1931

Didacna eichwaldi is a brackish-water bivalve mollusc of the family Cardiidae, the cockles. It has an oval-triangular, rather thick, whitish or cream shell, up to 40–55 mm (1.6–2.2 in) in length, with flattened ribs and a distinctly sharp posterior ridge in juvenile individuals, which can be seen on the umbo in adults. The species is endemic to the Caspian Sea. It lives in the middle and southern parts of the lake at depths down to 35 m (115 ft) and does not occur in desalinated areas.

Description

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Didacna eichwaldi has an oval-triangular, rather thick, convex shell, with a moderately or strongly protruding umbo, 21–34 flattened radial ribs and a distinctly sharp posterior ridge in juvenile individuals, which can be seen on the umbo in adults. The shell length is up to 40–55 mm (1.6–2.2 in) and the height is up to 30–45 mm (1.2–1.8 in). The coloration is whitish or cream.[1][2][3]

Differences from similar species

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Didacna baeri has a more rounded oval shell, with a less protruding umbo and a smooth posterior ridge, which is not sharp in juveniles.[2][3]

Several fossil species resemble D. eichwaldi. Didacna nalivkini has a less elongated shell, with a less distinct posterior ridge on the umbo. Didacna eulachia differs by a more elongated and less equilateral shell, with a larger number of ribs.[1] Didacna ovatocrassa has a less protruding umbo and a less distinct posterior ridge. The shell of Didacna subcrassa is less elongated.[2]

Distribution and ecology

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Didacna eichwaldi is endemic to the Caspian Sea. It lives in the middle and southern parts of the lake at depths down to 35 m (115 ft) and does not occur in desalinated areas.[4][5]

Fossil record

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Didacna eichwaldi is widespread in the Holocene (Neocaspian) deposits on the coasts of the middle and southern parts of the Caspian Sea. The oldest records date to the Late Pleistocene (Upper Khvalynian deposits).[4]

Taxonomy

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Illustrations of Didacna crassa from Eichwald's publication (1841)

The species was first described as Cardium crassum by Karl Eichwald in 1829, who never observed living individuals of this bivalve and only found numerous empty shells.[6] In 1838 he transferred it to the newly described genus Didacna[7] and in 1841 he published the first illustations of the species,[3] commenting on how it seemingly "died out only a century ago".[8]

The type locality of the species as indicated by Eichwald is "Caspium mare" (Caspian Sea). The type specimens have not been located.[3]

The original name of this species is a junior homonym of Cardium crassum Gmelin, 1791. In 1837 Ivan Andreevich Krynicki introduced a replacement name, Cardium eichwaldi.[9] Despite this, Eichwald and many subsequent authors referred to the species under the invalid name Didacna crassa.[5]

Logvinenko and Starobogatov (1969) treated this species as a junior synonym of D. baeri.[10] This synonymy was followed in catalogues of extant molluscs of Russia[11][12] and by Kijashko (2013),[13] but was not accepted by some other authors such as Yanina (2005)[14] and Nevesskaja (2007).[2] Wesselingh et al. (2019) and subsequent authors treated these species as distinct due to differences in shell characteristics.[3][5][15]

Didacna pseudoprotracta is an extinct species described by Livental (1931) from the Middle Pleistocene (Chaudian) deposits of the Chauda Cape (Kerch Peninsula, Crimea) and Guria (Georgia). He noted that the species resembles the extant Didacna protracta, but is probably more closely related to the extinct Didacna pseudocrassa.[16] Nevesskaja (1963) regarded D. pseudoprotracta as a synonym of D. crassa, although in her view D. crassa was present in the Pleistocene of the Black Sea region and was classified into multiple fossil subspecies (such as D. crassa guriensis)[17] which are now recognized as distinct species.[2][18] J. J. ter Poorten (2024) listed D. pseudoprotracta as a questionable synonym of D. eichwaldi.[3]

References

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  1. ^ a b Yanina 2005, p. 242.
  2. ^ a b c d e Nevesskaja, L. A. (2007). "History of the genus Didacna (Bivalvia: Cardiidae)". Paleontological Journal. 41 (9): 861–949. Bibcode:2007PalJ...41..861N. doi:10.1134/s0031030107090018.
  3. ^ a b c d e f ter Poorten, J. J. (2024). A taxonomic iconography of living Cardiidae. Harxheim: ConchBooks. p. 158. ISBN 978-3-948603-48-9.
  4. ^ a b Yanina 2005, p. 243.
  5. ^ a b c Wesselingh, F. P.; Neubauer, T. A.; Anistratenko, V. V.; Vinarski, M.; Yanina, T.; ter Poorten, J. J.; Kijashko, P.; Albrecht, C.; Anistratenko, O. Y.; D'Hont, A.; Frolov, P.; Gándara, A. M.; Gittenberger, A.; Gogaladze, A.; Karpinsky, M.; Lattuada, M.; Popa, L.; Sands, A. F.; van de Velde, S.; Vandendorpe, J.; Wilke, T. (2019). "Mollusc species from the Pontocaspian region – an expert opinion list". ZooKeys (827): 31–124. Bibcode:2019ZooK..827...31W. doi:10.3897/zookeys.827.31365. PMC 6472301. PMID 31114425.
  6. ^ Eichwald, E. (1829). Zoologia Specialis quam expositis animalibus tum vivis, tum fossilibus potissimum Rossiae in universum, et Poloniae in specie, in usum lectionum publicarum in Universitate Caesarea Vilnensi habendarum. Pars prior. Propaedeuticam Zoologiae atque specialem Heterozoorum expositionem continens (in Latin). Vilnius: Joseph Zawadzki. p. 283.
  7. ^ Eichwald, E. (1838). "Faunae Caspii Maris primitiae". Bulletin de la Société Impériale des Naturalistes de Moscou (in Latin). 11 (2): 125–174.
  8. ^ Eichwald, E. (1841). Fauna Caspio-Caucasia nonnullis observationibus novis illustravit (in Latin). Petropoli: Litteris Typographiae Dairii Gall. Politic. Petropol. p. 273.
  9. ^ Krynicki, I. A. (1837). "Conchylia tam terrestria, quam fluviatilia et e maribus adjacentibus Imperii Rossici indigena, quae pro mutua offeruntur historiae naturalis cultoribus commutatione". Bulletin de la Société Impériale des Naturalistes de Moscou (in Latin). 10 (2): 50–64.
  10. ^ Logvinenko, B. M.; Starobogatov, Y. I. (1969). "Tip Mollyuski. Mollusca" [Phylum Molluscs. Mollusca]. In Birshteyn, Y. A.; Vinogradov, L. G.; Kondakov, N. N.; Kuhn, M. S.; Astakhova, T. V.; Romanova, N. N. (eds.). Atlas bespozvonochnykh Kaspiyskogo morya [Atlas of the Invertebrates of the Caspian Sea] (in Russian). Moscow: Pishchevaya Promyshlennost. p. 324.
  11. ^ Kantor, Y. I.; Sysoev, A. V. (2005). Catalogue of molluscs of Russia and adjacent countries (in Russian). Moscow: KMK Scientific Press Ltd. p. 353. ISBN 5-87317-191-2.
  12. ^ Vinarski, M. V.; Kantor, Y. I. (2016). Analytical catalogue of fresh and brackish water molluscs of Russia and adjacent countries. Moscow: A. N. Severtsov Institute of Ecology and Evolution of Russian Academy of Sciences. p. 71. ISBN 978-5-9908840-7-6.
  13. ^ Kijashko, P. V. (2013). "Mollyuski Kaspiyskogo morya" [Molluscs of the Caspian sea]. In Bogutskaya, N. G.; Kijashko, P. V.; Naseka, A. M.; Orlova, M. I. (eds.). Identification keys for fish and invertebrates of the Caspian Sea (in Russian). Vol. 1. Fish and molluscs. St. Petersburg; Moscow: KMK Scientific Press Ltd. p. 352. ISBN 978-5-87317-932-9.
  14. ^ Yanina 2005, pp. 242–243.
  15. ^ Vinarski, M. V.; Kijashko, P. V.; Andreeva, S. I.; Sitnikova, T. Y.; Yanina, T. A. (2024). "Atlas and catalogue of the living mollusks of the Aral and Caspian Seas". Vita Malacologica. 23: 1–124. ISBN 978-3-948603-50-2.
  16. ^ Livental, V. E. (1931). "Geologicheskiye issledovaniya v yugo-zapadnoy chasti Guriyskogo neftenosnogo rayona" [Geological research in the southwestern part of the Guria oil-bearing region]. Trudy Azerbaidzhanskogo Neftyanogo issledovatel'skogo Instituta (in Russian). 2: 1–44.
  17. ^ Nevesskaja, L. A. (1963). "Opredelitel' dvustvorchatykh mollyuskov morskikh chetvertichnykh otlozheniy Chernomorskogo basseyna" [Key to bivalve molluscs of marine Quaternary sediments of the Black Sea basin]. Trudy Paleontologicheskogo Instituta (in Russian). 96: 1–211.
  18. ^ Yanina 2005, p. 226.

Cited texts

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  • Yanina, Т. А. (2005). Didakny Ponto-Kaspiya [Didacnas of the Ponto-Caspian Region] (in Russian). Smolensk: Majenta. ISBN 5-98156-024-X.
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