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Didacna trigonoides

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Didacna trigonoides
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Cardiida
Family: Cardiidae
Genus: Didacna
Species:
D. trigonoides
Binomial name
Didacna trigonoides
(Pallas, 1771)
Synonyms
  • Cardium trilaterum Gmelin, 1791
  • Didacna trigonoides tuzetae Tadjalli-Pour, 1977

Didacna trigonoides is a brackish-water cockle, a bivalve mollusc of the family Cardiidae. It has a whitish or cream oval-triangular shell, up to 40–65 mm in length, with tan or reddish brown flattened ribs. The species is endemic to the Caspian Sea. It is a sedentary filter feeder that lives at depths from 3 to 60 m and feeds on suspended algae and mollusc larvae.

Description

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Didacna trigonoides has a rather thick and convex oval-triangular shell, with a strongly protruding umbo and 20–30 tan or reddish brown flattened radial ribs.[1][2][3] The shell length is up to 40–65 mm,[4] the height is up to 40 mm, and the convexity is up to 30–33 mm.[5] The juveniles have a distinct and often double ridged posterior keel which becomes weaker with age.[3][6] The coloration is whitish or cream, with thin greyish brown to orange-brown periostracum on the exterior and a posterior reddish brown stain on the interior. The right valve has a poorly developed posterior lateral tooth.[3]

Differences from other species

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Didacna pyramidata has a less convex shell, with a less protruding umbo, more ribs and a stronger lateral tooth.[3]

Shell of the extinct Didacna praetrigonoides has more ribs and a less pronounced triangular shape.[4][6]

The extinct Didacna subpyramidata has a less elongated shell with a less protruding umbo.[4]

Distribution

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D. trigonoides is endemic to the Caspian Sea.[7] It occurs in all parts of the sea and is the only species of its genus that is widespread in the Northern Caspian.[3][5][8]

Ecology

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The species is a sedentary filter feeder[9] that lives on sandy, shelly and mixed hard substrates[5] at depths from 3 to 60 m.[3] It favors waters with salinity of 7–12‰, can tolerate salinity levels of 4–7‰ and 12–15‰, while levels of 2,3‰ and over 15‰ are lethal to it.[9]

The adults of D. trigonoides burrow halfway into the sediment while the juveniles fully bury themselves, leaving a small part of their shell on the surface. In this position the short and immobile siphons of this cockle are always pointed upwards. It feeds on suspended algae but larger specimens can also consume mollusc larvae.[9]

Fossil record

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D. trigonoides is widespread in the Holocene deposits of the Caspian Sea.[6] Nevesskaja (2007) hypothesized that it descended from the Late Pleistocene D. praetrigonoides.[4]

Taxonomy

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The species was first described as Cardium trigonoides by Peter Simon Pallas in 1771 who called it "the most numerous shell of the Caspian Sea" but found no living specimens.[10] In 1838 Karl Eichwald transferred it to the newly described genus Didacna and considered it an extinct species.[11] Subsequently, D. trigonoides has been designated as the type species of its genus by Stoliczka (1870).[12]

The type locality of D. trigonoides as indicated by Pallas is "Maris Caspii" (Caspian Sea).[3] The original type specimens are lost. One specimen from the Paleontological Institute of the Russian Academy of Sciences, collected by Nicolai Ivanovich Andrusov on the beach of Chechen Island, was designated as the neotype of this species by Nevesskaja (2007).[4]

Svitoch (1967) described two fossil subspecies of D. trigonoides: D. trigonoides chasarica from the Middle Pleistocene and D. trigonoides chvalynica from the Late Pleistocene.[13] Yanina (2005) synonymized the latter subspecies with the extinct Didacna ebersini[14] while Nevesskaja (2007) treated it as a tentative synonym of D. ebersini and D. praetrigonoides praetrigonoides.[4]

Synonyms

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In 1791 Johann Friedrich Gmelin described the species Cardium trilaterum from the Caspian Sea.[15] It is now considered to be a synonym of D. trigonoides.[16][17]

Didacna trigonoides tuzetae is a subspecies described by Tadjalli-Pour (1977) from Iran.[18] J. J. ter Poorten (2024) regarded it as a questionable synonym of D. trigonoides.[3]

References

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  1. ^ 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. 323.
  2. ^ Yanina 2005, p. 244.
  3. ^ a b c d e f g h ter Poorten, J. J. (2024). A taxonomic iconography of living Cardiidae. Harxheim: ConchBooks. p. 156. ISBN 978-3-948603-48-9.
  4. ^ a b c d e f 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.
  5. ^ a b c Zhadin, V. I. (1952). Mollyuski presnykh i solonovatykh vod SSSR [Molluscs of Fresh and Brackish Waters of the USSR] (PDF). Opredeliteli po faune SSSR, izdavayemyye Zoologicheskim institutom AN (in Russian). Vol. 46. Moscow–Leningrad: The USSR Academy of Sciences Press. p. 346. Archived (PDF) from the original on 2 December 2024.
  6. ^ a b c Yanina 2005, p. 245.
  7. ^ Kijashko 2013, p. 358.
  8. ^ Kijashko 2013, p. 344.
  9. ^ a b c Akhvlediani, E. G. (1966). "Rod Didacna" [Genus Didacna]. In Davitashvili, L. S; Merklin, R. L (eds.). Spravochnik po ekologii morskikh dvustvorok [Handbook on the ecology of marine bivalves] (in Russian). Moscow: Nauka. pp. 167–171.
  10. ^ Pallas, P. S. (1771). Reise durch verschiedene Provinzen des Russischen Reichs. Theil 1. Physicalische Reise durch verschiedene Provinzen des Russischen Reichs im 1768- und 1769 sten Jahren. St. Petersburg: Kayserliche Akademie der Wissenschaften. p. 478.
  11. ^ Eichwald, E. (1838). "Faunae Caspii Maris primitiae". Bulletin de la Société Impériale des Naturalistes de Moscou (in Latin). 11 (2): 125–174.
  12. ^ Stoliczka, F. (1870). "Cretaceous fauna of southern India". Memoirs of the Geological Society of India, 5. Palaeontologica Indica, Series 6. 3: 1–222.
  13. ^ Svitoch, A. A. (1967). Atlas-opredelitel' mollyuskov r. Didacna Eichwald iz chetvertichnyh otlozheniy Tsentral'nogo Prikaspiya [Atlas and Key to Molluscs of the Genus Didacna Eichwald from Quaternary Deposits of the Central Caspian Region] (in Russian). Moskva: Nedra. pp. 38–40.
  14. ^ Yanina 2005, p. 239.
  15. ^ Gmelin, J. F. (1791). Vermes. Caroli a Linnaei Systema Naturae per Regna Tria Naturae, Ed. 13. Tome 1(6) (in Latin). Lipsiae: G. E. Beer. pp. 3021–3910.
  16. ^ Kijashko 2013, p. 37.
  17. ^ 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. 70. ISBN 978-5-9908840-7-6.
  18. ^ Tadjalli-Pour, M. (1977). "Les Mollusques marins des côtes Iraniennes de la Mer Caspienne (Astara-Hachtpar)". Journal de Conchyliologie (in French). 114 (3–4): 87–117.

Cited texts

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  • 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. pp. 298–392. ISBN 978-5-87317-932-9.
  • 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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