Biology:Adacna fragilis

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Short description: Species of brackish-water bivalve

Adacna fragilis
Shell of Adacna fragilis from the Taganrog Bay (Merzhanovo, Russia)
Scientific classification edit
Missing taxonomy template (fix): Adacna
Species:
Template:Taxonomy/AdacnaA. fragilis
Binomial name
Template:Taxonomy/AdacnaAdacna fragilis
Milaschewitsch, 1908

Adacna fragilis is a brackish-water bivalve mollusc of the family Cardiidae, the cockles. It has an oval, thin, white, pale yellow or brownish shell, up to 20–33 mm (0.79–1.30 in) in length, with irregularly placed ribs. The species is endemic to the Black Sea Basin, where it lives in shallow inshore habitats in estuaries and limans and burrows deep into soft sediments. It is native to some of the lakes of the Danube Delta, the Kuchurgan, Dniester and Dnieper-Bug limans as well as the Taganrog Bay of the Sea of Azov. By the 21st century the species have severely declined in some of these areas due to human activity, becoming locally extinct in the Razelm-Sinoe Lake complex, the Kuchurgan Liman and, possibly, in the Dnieper-Bug Liman. Large populations of A. fragilis still occur in the Taganrog Bay.

Description

Adacna fragilis has an oval, thin, compressed shell, with a slightly anteriorly displaced umbo, about 23–32 irregularly placed radial ribs, which are usually more pronounced on the middle part of the shell, and a deep pallial sinus, which does not reach the vertical midline of the shell. The shell length is up to 20–33 mm (0.79–1.30 in). The valves are slightly gaping at the anterior and posterior margins. The coloration is white, pale yellow or brownish, with very thin yellowish gray-tan periostracum. The hinge has no teeth.[1][2]

Fully extended siphons of this species are significantly longer than its shell. The foot is weakly developed.[2]

Differences from similar species

Adacna vitrea has much weaker developed ribs and its coloration is often partially pinkish or purple.[2]

Adacna laeviuscula from the Caspian Sea is a larger species, with a less symmetrical shell, slightly less ribs and a pallial sinus which extends up to half of the shell length.[2]

Distribution and ecology

The Taganrog Bay is one of the only habitats where Adacna fragilis still occurs in large numbers.

Adacna fragilis is endemic to the Black Sea Basin.[2] It lives in shallow inshore habitats in estuaries and limans and burrows deep into soft sediments.[1][2][3] The species is native to lakes Kagul, Yalpuh and Katlabukh,[4] the Razelm-Sinoe Lake complex (Danube Delta),[5] the Kuchurgan,[6] Dniester and Dnieper-Bug limans as well as the Taganrog Bay of the Sea of Azov.[1][5]

In the Razelm-Sinoe Lake complex, the Dniester and Dnieper-Bug limans A. fragilis have formed relatively species-poor communities together with the cockles Monodacna colorata and Hypanis plicata. However, by the 21st century these communities have disappeared as populations of A. fragilis and H. plicata have largely declined due to human activity and the latter species possibly became extinct in the Black Sea Basin. Both species used to be common in the Razelm-Sinoe Lake complex but rerouting of the Danube and closing of the Black Sea inlets in the second half of the 20th century caused the disappearance of most brackish water molluscs except for M. colorata.[5] Reports of A. fragilis from this area in 2002–2004[7] are unconfirmed[2] and later records in 2007–2008[8] are misidentifications of M. colorata.[9] In the Kuchurgan Liman A. fragilis was still recorded in 1966–1970 but disappeared as the liman was turned into a cooling pond in 1981–1984.[10] In the Dniester Liman the species declined due to salinity regime changes caused by human activity. For similar reasons, it became very rare or locally extinct in the Dnieper-Bug Liman. Large populations of A. fragilis still occur in the Taganrog Bay.[5]

A. fragilis (together with M. colorata) became abundant in the Sasyk Lake, which was previously inhabited by marine communities but was transformed into a brackish water reservoir after getting connected to the Danube, via a canal, in 1978.[5][11] The species was also reported from the Kremenchuk Reservoir of the Dnieper River.[12]

Conservation

Although the conservation status of A. fragilis has not been assessed by the International Union for Conservation of Nature,[13] the species has been included in the Red Data Book of Ukraine under the Vulnerable category (as Hypanis laeviuscula)[14] and in the Red Book of Moldova under the Critically Endangered category (as H. laeviuscula fragilis).[15]

Taxonomy

Adacna fragilis was first described from the Dniester Liman and the Katlabukh Lake by a Russian geologist and paleontologist Konstantin Osipovich Milaschewitsch in 1908.[16] The type specimens have not been traced.[13]

Zhadin (1952) treated this species as a variety of A. laeviuscula,[17] while Scarlato and Starobogatov (1972) regarded it as a subspecies (as Hypanis laeviuscula fragilis).[1] Starobogatov et al. (2004) have once again recognized A. fragilis as a distinct species,[3] but later authors believed that it could be a synonym of A. laeviuscula and its taxonomic status was listed as uncertain by Wesselingh et al. (2019).[18] Studies by Gogaladze et al. (2021) have shown that A. fragilis is a distinct species from the Caspian A. laeviuscula as they differ by shell characteristics and salinity preferences.[5]

References

  1. ↑ 1.0 1.1 1.2 1.3 Scarlato, O. A.; Starobogatov, Y. I. (1972). "Klass dvustvorchatyye mollyuski — Bivalvia" (in ru). Opredelitel' fauny Chernogo i Azovskogo morey. 3. Kiev: Naukova Dumka. p. 216. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 ter Poorten 2024, p. 152.
  3. ↑ 3.0 3.1 Starobogatov, Y. I.; Bogatov, V. V.; Prozorova, L. A.; Saenko, E. M. (2004). "Molluscs" (in ru). Key to Freshwater Invertebrates of Russia and Adjacent Lands. 6. Molluscs, Polychaetes, Nemerteans. Saint-Petersburg: Nauka. p. 49. ISBN 5-02-026204-8. 
  4. ↑ Markovsky, Y. M. (1955) (in ru). Fauna bespozvonochnykh nizov'ev rek Ukrainy, usloviya yeyo sushchestvovaniya i puti ispol'zovaniya. Chast' 3. Vodoemy Kilijskoy delty Dunaya. Kyiv: AN SSSR. p. 57. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Gogaladze, A.; Son, M. O.; Lattuada, M.; Anistratenko, V. V.; Syomin, V. L.; Pavel, A. B.; Popa, O. P.; Popa, L. O. et al. (2021). "Decline of unique Pontocaspian biodiversity in the Black Sea Basin: A review". Ecology and Evolution 11 (19): 12923–12947. doi:10.1002/ece3.8022. PMID 34646444. PMC 8495785. Bibcode: 2021EcoEv..1112923G. https://onlinelibrary.wiley.com/doi/10.1002/ece3.8022. 
  6. ↑ Markovsky, Y. M. (1953) (in ru). Fauna bespozvonochnykh nizov'ev rek Ukrainy, usloviya yeyo sushchestvovaniya i puti ispol'zovaniya. Chast' 1. Vodoemy delty Dnestra i Dnestrovskiy liman. Kyiv: AN SSSR. p. 29. 
  7. ↑ Begun, T.; Teaca, A.; Muresan, M.; Pavel, A. B. (2020). "Current state of the mollusc populations in the Razim-Sinoe Lagoon system". Scientific Papers. Series D. Animal Science 63 (1): 553–561. https://animalsciencejournal.usamv.ro/pdf/2020/issue_1/Art81.pdf. 
  8. ↑ Popa, O. P.; Sárkány-Kiss, A.; Kelemen, B.; Iorgu, E. I.; Murariu, D.; Popa, L. O. (2009). "Contributions to the knowledge of the present Limnocardiinae fauna (Mollusca: Bivalvia) from Romania". Travaux du Muséum National d'Histoire Naturelle "Grigore Antipa" 52: 7–15. 
  9. ↑ ter Poorten 2024, p. 142.
  10. ↑ Filipenko, S. (2023) (in ru). Zoobentos Dubossarskogo i Kuchurganskogo vodokhranilishch. Chișinău: self-published. pp. 50–55. ISBN 978-9975-3610-1-9. https://eco-tiras.org/books/Filipenco-book-Benthos-Dubasari%20and%20Cuciurgan%202023.pdf. 
  11. ↑ Khalaim, A. A.; Son, M. O. (2016). "Biological and ecological characteristics of Hypanis laeviuscula fragilis (Milachevitch, 1908) (Mollusca, Cardiidae) from Sasyk Reservoir" (in ru). Uzhgorod University Scientific Bulletin: Series: Biology 41: 59–63. https://dspace.uzhnu.edu.ua/jspui/bitstream/lib/23407/1/%d0%91%d0%98%d0%9e%d0%9b%d0%9e%d0%93%d0%9e-%d0%ad%d0%9a%d0%9e%d0%9b%d0%9e%d0%93%d0%98%d0%a7%d0%95%d0%a1%d0%9a%d0%90%d0%af%20%d0%a5%d0%90%d0%a0%d0%90%d0%9a%d0%a2%d0%95%d0%a0%d0%98%d0%a1%d0%a2%d0%98%d0%9a%d0%90.pdf. 
  12. ↑ Munasypova-Motyash, I. A. (2006). "O sovremennoy faune dvustvorchatykh mollyuskov podsemeistva Limnocardiinae (Bivalvia, Cardiidae) Severo-Zapadnogo Prichernomorya" (in ru). Vestnik Zoologii 40 (1): 41–48. https://www.v-zool.kiev.ua/pdfs/2006/1/03_Munasipova.pdf. 
  13. ↑ 13.0 13.1 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. 64. ISBN 978-5-9908840-7-6. 
  14. ↑ Munasypova-Motyash, I. A. (2009). "Hipanis leviuskula Hypanis laeviuscula". in Akimov, I. A. (in uk). Chervona knyha Ukrayiny. Tvarynnyy svit (Third ed.). Kyiv: Globalconsulting. p. 306. ISBN 978-966-97059-0-7. 
  15. ↑ Toderas, I.; Munjiu, O.; Subernetki, I. (2015). "Hypanis laeviuscula fragilis (Milasch., 1908) – Hipanis-neted-fragil". The Red Book of the Republic of Moldova (Third ed.). Ştiinţa. p. 467. ISBN 978-9975-67-998-5. https://zoology.md/sites/default/files/inline-files/Cartea%20Rosie_Partea%20II%20Animale_1.pdf. 
  16. ↑ Milaschewitsch, K. O. (1908). "Mollyuski, sobrannyye vo vremya ekskursii S.A. Zernova na minonostse № 264 na r. Dunay s 28 iyunya po 3 iyulya 1907 g." (in ru). Bulletin de l'Académie Impériale des Sciences de St.-Pétersbourg. 6 2 (12): 991–996. https://www.mathnet.ru/links/91aa4ef1285f597c46827c681c8ad930/im7445.pdf. 
  17. ↑ 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. p. 354. https://www.zin.ru/publications/fauna_keys/keys_46_zhadin_1952.pdf. 
  18. ↑ 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. 

Cited texts

  • ter Poorten, J. J. (2024). A taxonomic iconography of living Cardiidae. Harxheim: ConchBooks. ISBN 978-3-948603-48-9. 

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