Biology:Didacna trigonoides

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Short description: Species of brackish-water bivalve

Didacna trigonoides
Illustrations of Cardium trigonoides from Lovell Reeve's Conchologia Iconica (1844)[1]
Scientific classification edit
Missing taxonomy template (fix): Didacna
Species:
Template:Taxonomy/DidacnaD. trigonoides
Binomial name
Template:Taxonomy/DidacnaDidacna trigonoides
(Pallas, 1771)
Synonyms
  • Cardium trilaterum Gmelin, 1791
  • Tadjalli-Pour, 1977 Didacna trigonoides tuzetae

Didacna trigonoides is a brackish-water bivalve mollusc of the family Cardiidae, the cockles. It has an oval-triangular, thick, whitish or cream shell, up to 40–65 mm (1.6–2.6 in) in length, with flattened tan or reddish brown ribs. The species is endemic to the Caspian Sea. It is a sedentary filter feeder that lives at depths from 3 to 60 m (9.8–196.9 ft) and feeds on suspended algae and mollusc larvae.

Description

Didacna trigonoides has an oval-triangular, thick, convex shell, with a strongly protruding umbo, 20–30 flattened tan or reddish brown radial ribs and a posterior keel, which is distinct and often double ridged in juveniles, but becomes weaker with age.[2][3][4][5] The shell length is up to 40–65 mm (1.6–2.6 in).[6] The external coloration is whitish or cream, with thin greyish brown to orange-brown periostracum. The interior is white, with a reddish brown stain on the posterior margin.[5] The hinge consists of two cardinal teeth in both valves[2][7] and a weakly developed posterior lateral tooth in the right valve.[5]

Similar species

Didacna barbotdemarnii differs from juvenile D. trigonoides by a more elongated and less convex shell, with slightly more ribs.[8]

Didacna pyramidata has a less inflated shell, with a lower umbo, more ribs and a stronger lateral tooth.[5]

Didacna praetrigonoides is a possibly extinct species mainly known from the Late Pleistocene deposits of the Caspian Sea and whose shells occasionally wash ashore.[9] It differs from D. trigonoides by a larger number of ribs and a less pronounced triangular shape.[6][10]

The fossil species Didacna subpyramidata has a less elongated shell and a lower umbo.[6]

Distribution

Didacna trigonoides is endemic to the Caspian Sea.[11] It occurs in all parts of the sea and is the only species of its genus that is widespread in the Northern Caspian.[2][5][12]

Ecology

Didacna trigonoides is a sedentary filter feeder[13] that lives on sandy, shelly and mixed hard substrates[2] at depths from 3 to 60 m (9.8–196.9 ft).[5] 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. The adults 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 bivalve are always pointed upwards. It feeds on suspended algae, but larger specimens can also consume mollusc larvae.[13]

Fossil record

Didacna trigonoides is widespread in the Holocene deposits of the Caspian Sea.[10] Nevesskaja (2007) hypothesized that the species descended from the Late Pleistocene D. praetrigonoides.[6]

Taxonomy

Drawings of Didacna trigonoides from Eichwald's publication (1841)[14]

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.[15] In 1838 Karl Eichwald transferred it to the newly described genus Didacna.[16] Subsequently, D. trigonoides has been designated as the type species of its genus by Stoliczka (1870).[17][18]

The type locality of D. trigonoides as indicated by Pallas is "Maris Caspii" (Caspian Sea).[5] 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).[6]

Svitoch (1967) described two fossil subspecies of D. trigonoides: D. trigonoides chasarica from the Middle Pleistocene and D. trigonoides chvalynica from the Late Pleistocene.[19] Yanina (2005) synonymized the latter subspecies with the extinct Didacna ebersini,[20] while Nevesskaja (2007) treated it as a tentative synonym of D. ebersini and D. praetrigonoides praetrigonoides.[6]

Synonyms

In 1791 Johann Friedrich Gmelin described the species Cardium trilaterum from the Caspian Sea.[21] It is now considered to be a synonym of D. trigonoides.[22]

Didacna trigonoides tuzetae is a subspecies described by Tadjalli-Pour (1977) from Iran.[23] Wesselingh et al. (2019) synonymized it with D. trigonoides.[9]

References

  1. ↑ Reeve, L. A. (1844–1845). "Monograph of the genus Cardium". Conchologia Iconica, or, illustrations of the shells of molluscous animals. 2. London: Reeve & Co.. http://biodiversitylibrary.org/page/8937393. 
  2. ↑ 2.0 2.1 2.2 2.3 Zhadin, V. I. (1952) (in ru). Mollyuski presnykh i solonovatykh vod SSSR. Opredeliteli po faune SSSR, izdavayemyye Zoologicheskim institutom AN. 46. Moscow–Leningrad: The USSR Academy of Sciences Press. pp. 346. https://www.zin.ru/publications/fauna_keys/keys_46_zhadin_1952.pdf. 
  3. ↑ Logvinenko, B. M.; Starobogatov, Y. I. (1969). "Tip Mollyuski. Mollusca" (in ru). Atlas bespozvonochnykh Kaspiyskogo morya. Moscow: Pishchevaya Promyshlennost. p. 323. 
  4. ↑ Yanina 2005, pp. 244–245.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 ter Poorten 2024, p. 156.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Nevesskaja, L. A. (2007). "History of the genus Didacna (Bivalvia: Cardiidae)". Paleontological Journal 41 (9): 861–949. doi:10.1134/s0031030107090018. Bibcode: 2007PalJ...41..861N. 
  7. ↑ Yanina 2005, pp. 244.
  8. ↑ ter Poorten 2024, p. 162.
  9. ↑ 9.0 9.1 Wesselingh, F. P.; Neubauer, T. A.; Anistratenko, V. V.; Vinarski, M.; Yanina, T.; ter Poorten, J. J.; Kijashko, P.; Albrecht, C. et al. (2019). "Mollusc species from the Pontocaspian region – an expert opinion list". ZooKeys (827): 31–124. doi:10.3897/zookeys.827.31365. PMID 31114425. PMC 6472301. Bibcode: 2019ZooK..827...31W. https://zookeys.pensoft.net/article/31365. 
  10. ↑ 10.0 10.1 Yanina 2005, p. 245.
  11. ↑ Kijashko 2013, p. 358.
  12. ↑ Kijashko 2013, p. 344.
  13. ↑ 13.0 13.1 Akhvlediani, E. G. (1966). "Rod Didacna" (in ru). Spravochnik po ekologii morskikh dvustvorok. Moscow: Nauka. pp. 167–171. 
  14. ↑ Eichwald, E. (1841) (in la). Fauna Caspio-Caucasia nonnullis observationibus novis illustravit. Petropoli: Litteris Typographiae Dairii Gall. Politic. Petropol.. https://www.biodiversitylibrary.org/item/219319. 
  15. ↑ 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. http://resolver.sub.uni-goettingen.de/purl?PPN329913735. 
  16. ↑ Eichwald, E. (1838). "Faunae Caspii Maris primitiae". Bulletin de la Société Impériale des Naturalistes de Moscou 11 (2): 125–174. https://www.biodiversitylibrary.org/page/41342125. 
  17. ↑ Stoliczka, F. (1870). "Cretaceous fauna of southern India". Memoirs of the Geological Society of India, 5. Palaeontologica Indica. Series 6 3: 1–222. http://www.biodiversitylibrary.org/item/110955. 
  18. ↑ Kantor, Y. I.; Sysoev, A. V. (2005) (in ru). Catalogue of molluscs of Russia and adjacent countries. Moscow: KMK Scientific Press Ltd.. p. 353. ISBN 5-87317-191-2. 
  19. ↑ Svitoch, A. A. (1967) (in ru). Atlas-opredelitel' mollyuskov r. Didacna Eichwald iz chetvertichnyh otlozheniy Tsentral'nogo Prikaspiya. Moskva: Nedra. pp. 38–40. 
  20. ↑ Yanina 2005, p. 239.
  21. ↑ Gmelin, J. F. (1791) (in la). Vermes. Caroli a Linnaei Systema Naturae per Regna Tria Naturae, Ed. 13. Tome 1(6). Lipsiae: G. E. Beer. pp. 3021–3910. https://www.biodiversitylibrary.org/item/83098. 
  22. ↑ 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. 
  23. ↑ Tadjalli-Pour, M. (1977). "Les Mollusques marins des côtes Iraniennes de la Mer Caspienne (Astara-Hachtpar)" (in fr). Journal de Conchyliologie 114 (3–4): 87–117. 

Cited texts

  • Kijashko, P. V. (2013). "Mollyuski Kaspiyskogo morya" (in ru). Identification keys for fish and invertebrates of the Caspian Sea. 1. Fish and molluscs. St. Petersburg; Moscow: KMK Scientific Press Ltd.. pp. 298–392. ISBN 978-5-87317-932-9. 
  • ter Poorten, J. J. (2024). A taxonomic iconography of living Cardiidae. Harxheim: ConchBooks. ISBN 978-3-948603-48-9. 
  • Yanina, Т. А. (2005) (in ru). Didakny Ponto-Kaspiya. Smolensk: Majenta. ISBN 5-98156-024-X. 

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