Adacna laeviuscula

Adacna laeviuscula has an irregularly oval, thin, compressed, semitranslucent shell, with a narrower anterior margin, an anteriorly displaced umbo, 20–29 flattened radial ribs, which are wider on the posterior half, and a wide and deep pallial sinus, which extends up to half of the shell length or is slightly deeper. The shell length is up to {{cvt|40–50|mm}}. The valves are strongly gaping at the anterior and posterior margins. The coloration is white, with very thin light yellowish periostracum. The hinge may have no teeth or a reduced cardinal tooth can be present in the right valve.{{sfn|Zhadin|1952|pp=353–354}}{{sfn|Logvinenko|Starobogatov|1969|p=337}}{{sfn|Kijashko|2013|pp=363, 377}}{{sfn|ter Poorten|2024|p=152}}

The siphons of this species are twice as long as its shell.{{sfn|Zhadin|1952|p=354}}

Smaller specimens of A. laeviuscula from the Northern Caspian Sea differ from Adacna vitrea glabra by more developed ribs.{{sfn|Logvinenko|Starobogatov|1969|p=337}}

Adacna fragilis, which inhabits lakes of the Danube Delta, estuaries of the Black Sea and the Taganrog Bay of the Sea of Azov, is a smaller sized species, with a more symmetrical shell, the pallial sinus of which does not extend up to half of the shell length. It also has slightly more ribs which are usually more pronounced on the middle part of the shell.{{sfn|ter Poorten|2024|p=152}}{{cite journal |last1=Gogaladze |first1=A. |last2=Son |first2=M. O. |last3=Lattuada |first3=M. |last4=Anistratenko |first4=V. V. |last5=Syomin |first5=V. L. |last6=Pavel |first6=A. B. |last7=Popa |first7=O. P. |last8=Popa |first8=L. O. |last9=ter Poorten |first9=J. J. |last10=Biesmeijer |first10=J. C. |last11=Raes |first11=N. |last12=Wilke |first12=T. |last13=Sands |first13=A. F. |last14=Trichkova |first14=T. |last15=Hubenov |first15=Z. K. |last16=Vinarski |first16=M. V. |last17=Anistratenko |first17=O. Y. |last18=Alexenko |first18=T. L. |last19=Wesselingh |first19=F. P. |date=2021 |title=Decline of unique Pontocaspian biodiversity in the Black Sea Basin: A review |journal=Ecology and Evolution |volume=11 |issue=19 |pages=12923–12947 |doi=10.1002/ece3.8022 |doi-access=free|pmid=34646444 |pmc=8495785 |bibcode=2021EcoEv..1112923G |hdl=1887/3238855 |hdl-access=free }}

Monodacna semipellucida has a broadly oval shell, with a shallower pallial sinus and reduced cardinal teeth in both valves.{{sfn|Logvinenko|Starobogatov|1969|p=336}}{{sfn|ter Poorten|2024|p=148}}

Adacna laeviuscula is endemic to the Caspian Sea.{{sfn|Kijashko|2013|p=377}} It lives at a salinity of at least 4‰{{sfn|Logvinenko|Starobogatov|1969|p=337}} at depths from 0 to 30 m (0 to 98 ft), rarely down to 60 m (197 ft).{{cite book |last1=Scarlato |first1=O. A. |last2=Starobogatov |first2=Y. I. |date=1972 |chapter=Klass dvustvorchatyye mollyuski — Bivalvia |trans-chapter=Class bivalve molluscs – Bivalvia |title=Opredelitel' fauny Chernogo i Azovskogo morey|trans-title=Guide to the fauna of the Black Sea and the Sea of Azov |editor-last1=Mordukhai-Boltovskoy |editor-first1=F. D. |volume=3 |location=Kiev |publisher=Naukova Dumka |page=216 |language=ru}} The species burrows into soft sediments.{{cite book|last1=Starobogatov|first1=Y. I.|last2=Bogatov|first2=V. V.|last3=Prozorova|first3=L. A.|last4=Saenko|first4=E. M.|date=2004|chapter=Molluscs|title=Key to Freshwater Invertebrates of Russia and Adjacent Lands|editor-last1=Tsalolikhin|editor-first1=S. J.|volume=6. Molluscs, Polychaetes, Nemerteans|location=Saint-Petersburg|publisher=Nauka|page=49|isbn=5-02-026204-8|language=ru}} Individuals from the Northern Caspian Sea in waters with salinity levels of 4–9‰ are smaller than those living in the central and southern parts of the sea at salinities of 12–14‰.{{sfn|Zhadin|1952|p=354}}

Despite earlier studies, Starobogatov et al. (2004) have reported that A. laeviuscula occurs at depths between 30 and 60 m (98 and 197 ft). However, fresh shells of this species with paired valves often wash up on beaches which indicates that it lives in shallow foreshore habitats.{{cite journal|last1=Wesselingh|first1=F. P.|last2=Neubauer|first2=T. A.|last3=Anistratenko|first3=V. V.|last4=Vinarski|first4=M.|last5=Yanina|first5=T.|last6=ter Poorten|first6=J. J.|last7=Kijashko|first7=P.|last8=Albrecht|first8=C.|last9=Anistratenko|first9=O. Y.|last10=D'Hont|first10=A.|last11=Frolov|first11=P.|last12=Gándara|first12=A. M.|last13=Gittenberger|first13=A.|last14=Gogaladze|first14=A.|last15=Karpinsky|first15=M.|last16=Lattuada|first16=M.|last17=Popa|first17=L.|last18=Sands|first18=A. F.|last19=van de Velde|first19=S.|last20=Vandendorpe|first20=J.|last21=Wilke|first21=T.|date=2019|title=Mollusc species from the Pontocaspian region – an expert opinion list|url=https://zookeys.pensoft.net/article/31365|journal=ZooKeys|issue=827|pages=31–124|doi=10.3897/zookeys.827.31365|doi-access=free|pmid=31114425 |pmc=6472301 |bibcode=2019ZooK..827...31W}}

Fossilized shells of Adacna laeviuscula occur in deposits of the Caspian Sea Basin since its Khazarian stage,{{cite journal|last1=Yanina|first1=T. A.|last2=Semikolennykh|first2=D. V.|last3=Sorokin|first3=V. M.|date=2024|title=Biodiversity of Malacofauna in the Caspian–Manych–Pont System in the Last Interglacial Era|journal=Arid Ecosystems|volume=14|number=2|pages=244–258|doi=10.1134/S2079096124700148}} which began 125,000–80,000 years ago during the Pleistocene.{{cite journal|last1=Krijgsman|first1=W.|last2=Tesakov|first2=A.|last3=Yanina|first3=T.|last4=Lazarev|first4=S.|last5=Danukalova|first5=G.|last6=Van Baak|first6=C. G. C.|last7=Agustí|first7=J.|last8=Alçiçek|first8=M. C.|last9=Aliyeva|first9=E.|last10=Bista|first10=D.|last11=Bruch|first11=A.|last12=Büyükmeriç|first12=Y.|last13=Bukhsianidze|first13=M.|last14=Flecker|first14=R.|last15=Frolov|first15=P.|last16=Hoyle|first16=T. M.|last17=Jorissen|first17=E. L.|last18=Kirscher|first18=U.|last19=Koriche|first19=S. A.|last20=Kroonenberg|first20=S. B.|last21=Lordkipanidze|first21=D.|last22=Oms|first22=O.|last23=Rausch|first23=L.|last24=Singarayer|first24=J.|last25=Stoica|first25=M.|last26=van de Velde|first26=S.|last27=Titov|first27=V. V.|last28=Wesselingh|first28=F. P.|date=2019|title=Quaternary time scales for the Pontocaspian domain: Interbasinal connectivity and faunal evolution|url=https://www.sciencedirect.com/science/article/pii/S001282521830415X?via%3Dihub|journal=Earth-Science Reviews|volume=188|pages=1–40|doi=10.1016/j.earscirev.2018.10.013|doi-access=free|hdl=20.500.11937/71421|hdl-access=free}} It has also been found in the Late Pleistocene of the Manych Depression where a strait connecting the Caspian and the Azov-Black Sea basins has repeatedly formed in the past.{{cite journal|last1=Svitoch|first1=A. A.|last2=Yanina|first2=T. A.|last3=Antonova|first3=V. M.|last4=van der Plicht|first4=J.|date=2008|title=The Khvalynian fauna of the Manych Depression|journal=Doklady Earth Sciences|volume=421|number=6|pages=987–991|doi=10.1134/S1028334X08060287}} Nevesskaja et al. (2001) hypothesized that the species could be a descendant of the extinct Monodacna praelaeviuscula from deposits of the Apsheronian Basin,{{cite journal|last1=Nevesskaja|first1=L. A.|last2=Paramonova |first2=N. P. |last3=Popov |first3=S. V. |date=2001 |title=History of Lymnocardiinae (Bivalvia, Cardiidae) |journal=Paleontological Journal |volume=35, Suppl. 3|pages=147–217}} which existed on the territory of the modern Caspian Sea from 1,8 or 2,1 million to 880,000–750,000 years ago.

File:Glycymeris laeviuscula.png

The species was first described as Glycymeris laeviuscula by Karl Eichwald in 1829.{{cite book|last=Eichwald|first=E.|date=1829|title=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|url=https://www.biodiversitylibrary.org/page/35882071|location=Vilnius|publisher=Joseph Zawadzki|page=279|language=la}} In 1838 he transferred it into the newly described genus Adacna.{{cite journal|last=Eichwald |first=E. |date=1838 |title=Faunae Caspii Maris primitiae |journal=Bulletin de la Société Impériale des Naturalistes de Moscou |volume=11 |number=2|pages=125–174|url=https://www.biodiversitylibrary.org/page/41342125}} Subsequently, Vest (1875) designated A. laeviuscula as the type species of its genus.{{cite journal|last=Vest |first=W. von. |date=1875 |title=Ueber die Genera Adacna, Monodacna und Didacna Eichwald und deren Stellung im System |journal=Jahrbücher der Deutschen Malakozoologischen Gesellschaft |volume=2 |pages=309–325|url=https://www.biodiversitylibrary.org/page/27002949|language=de}}{{cite book|last1=Kantor|first1=Y. I.|last2=Sysoev|first2=A. V.|date=2005|title=Catalogue of molluscs of Russia and adjacent countries|location=Moscow|publisher=KMK Scientific Press Ltd.|page=351|isbn=5-87317-191-2|language=ru}}

Eichwald initially reported Glycymeris laeviuscula from "the southern border of the Caspian Sea in bight of Astrabad" (Gorgan, Iran). However, one of the two shells collected by him in the Bay of Baku (Azerbaijan) was found to be identical to the original drawings of the species, apart from the fact that they depict a left valve while the actual specimen is a right valve. This specimen is now considered to be the lectotype of A. laeviuscula, and according to Article 76.2 of the International Code of Zoological Nomenclature, the Bay of Baku becomes the type locality of the species. The lectotype as well as the second specimen from this locality (the paralectotype) are both stored in the Zoological Institute of the Russian Academy of Sciences.{{sfn|Kijashko|2013|p=377}}{{cite journal|last1=Vinarski|first1=M. V.|last2=Kijashko|first2=P. V.|last3=Andreeva|first3=S. I.|last4=Sitnikova|first4=T. Y.|last5=Yanina|first5=T. A.|date=2024|title=Atlas and catalogue of the living mollusks of the Aral and Caspian Seas|journal=Vita Malacologica|volume=23|pages=1–124|isbn=978-3-948603-50-2}}

Jean Louis Rodolphe Agassiz, who was possibly unaware of Eichwald's works, redescribed the species as Pholadomya caspica in 1842.{{cite book|last=Agassiz|first=L.|date=1842|title=Études critiques sur les mollusques fossiles|volume=2|location=Neuchâtel|pages=45–48|url=https://www.biodiversitylibrary.org/page/2016095|language=fr}} This name is now regarded as a synonym of A. laeviuscula.

Adacna fragilis from the Black Sea Basin has sometimes been treated as a variety{{sfn|Zhadin|1952|p=354}} or a subspecies of A. laeviuscula.{{sfn|Logvinenko|Starobogatov|1969|p=337}} It was once again recognized as a distinct species by Starobogatov et al. (2004), but some 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). More detailed studies have shown that A. fragilis is a distinct species from the Caspian A. laeviuscula as they differ by shell characteristics and salinity preferences.

{{Reflist}}

• {{cite book|last=Kijashko|first=P. V.|date=2013|chapter=Mollyuski Kaspiyskogo morya|trans-chapter=Molluscs of the Caspian sea|title=Identification keys for fish and invertebrates of the Caspian Sea|editor-last1=Bogutskaya|editor-first1=N. G.|editor-last2=Kijashko|editor-first2=P. V.|editor-last3=Naseka|editor-first3=A. M.|editor-last4=Orlova|editor-first4=M. I.|volume=1. Fish and molluscs|location=St. Petersburg; Moscow|publisher=KMK Scientific Press Ltd.|pages=298–392|isbn=978-5-87317-932-9|language=ru}}
• {{cite book|last1=Logvinenko|first1=B. M.|last2=Starobogatov|first2=Y. I.|date=1969|chapter=Tip Mollyuski. Mollusca|trans-chapter=Phylum Molluscs. Mollusca|title=Atlas bespozvonochnykh Kaspiyskogo morya|trans-title=Atlas of the Invertebrates of the Caspian Sea|editor-last1=Birshteyn|editor-first1=Y. A.|editor-last2=Vinogradov|editor-first2=L. G.|editor-last3=Kondakov|editor-first3=N. N.|editor-last4=Kuhn|editor-first4=M. S.|editor-last5=Astakhova|editor-first5=T. V.|editor-last6=Romanova|editor-first6=N. N.|location=Moscow|publisher=Pishchevaya Promyshlennost|pages=308–385|language=ru}}
• {{cite book|last=ter Poorten|first=J. J.|date=2024|title=A taxonomic iconography of living Cardiidae|location=Harxheim|publisher=ConchBooks|isbn=978-3-948603-48-9}}
• {{cite book |last=Zhadin |first=V. I. | date=1952 |title=Mollyuski presnykh i solonovatykh vod SSSR |trans-title=Molluscs of Fresh and Brackish Waters of the USSR |url=https://www.zin.ru/publications/fauna_keys/keys_46_zhadin_1952.pdf |series=Opredeliteli po faune SSSR, izdavayemyye Zoologicheskim institutom AN |volume=46 |location=Moscow–Leningrad |publisher=The USSR Academy of Sciences Press |language=ru |url-status=live |archive-url=https://web.archive.org/web/20241202230923/https://www.zin.ru/publications/fauna_keys/keys_46_zhadin_1952.pdf |archive-date=2 December 2024}}

{{Taxonbar|from1=Q13228726}}

Category:Cardiidae

Category:Endemic fauna of the Caspian Sea

Category:Bivalves described in 1829

Category:Taxa named by Karl Eichwald