Dinaric cave clam Congeria kusceri, Bole 1962
Congeria kusceri (Dinaric cave clam) is the only underground bivalve in the world. It is a tertiary relic, the remnant of the Tertiary fauna which was able to survive to the present day, occupying the underground habitat. This way it survived the changes on the surface which led other species of Congeria to extinction. The entire genus was considered extinct until 1934 when the shells were found in spring Stinjevac near Vrgorac in Dalmatia. Based on them, Slovenian malacologist Ljudevit Kušcer assumed that Congeria still lives in the depths of the underground. However, the first live specimens were found in the Žira ponor in Popovo polje in Herzegovina by Jože Štirn. It was only in 1962 that the Slovenian malacologist Jože Bole described a new species Congeria kusceri.
Shells of the Dinaric cave clam size up to 20 mm, they are oval and the front end is elongated and tapering to a triangular and curved top. Both shells are very prominent and rounded, and without reefs. Both the tissue and the shells are depigmentated and statocyst as well as light receptors and reduced. It lives solitary or in groups. It is attached to the walls of underground channels by byssal threads. Feeding with fine organic particles occurs by filtering the water. The species is unisexual and fertilization is internal. Females guard the fertilized eggs on the gills until the development of the veliger larvae which after a short planktonic phase attaches to the hard surface or small bivalves are released directly from the gills. This species spends its entire lifespan in the underground (Morton, 1998).
Dinaric cave clam is endemic to Dinarides. It is known from one locality in Slovenia, but only the shells were found. It also lives in several localities in Bosnia and Herzegovina. In Croatia it is recorded in a total of fifteen localities, but at most sites only shells were found (Jalžic, 1998; Jalžic, 2001). Live populations were documented in only five sites, but the surveys in 2008 for the project Natura 2000 - Scientific analysis of groundwater species (Congeria kusceri and Leptodirus hochenvartii) listed in the Annex II of the Habitats Directive revealed that the two populations disappeared (Jalžic & Bilandžija, 2008). This is direct evidence that this is a critically endangered species, and if we do not take urgent measures it could be irretrievably lost. In the Red Book of Croatian cave fauna that is currently in preparation, Congeria kusceri is listed in the IUCN category of CR (critically endangered), which means that the risk of its disappearance in natural habitats is very high. The causes of its endangerment are manifold: pollution of groundwater due to the use of pesticides and fertilizers in agriculture, due to contamination from municipal and industrial wastewater and illegal waste disposal. Changes in groundwater regime occur due to hydrotehnical interventions including meliorations of karst fields, power plant constructions, uncontrolled extraction of groundwater reservoirs etc. This finally leads to the alterations of direction of groundwater flow and/or groundwater level changes. Backfilling of the caves due to the illegal construction and intensive urbanization is another problem for the survival of Congeria kusceri.
In addition to being protected by the Croatian law the Dinaric cave clam is listed in the Annexes II and IV of the Habitats Directive, i.e. defining the special areas of protection (SAC) as a part of the NATURA 2000 network is necessary for the protection of this species. Thus, 3 areas for protection have been proposed: Lika-Velebit region, Vrgorac region and Metkovic region (Jalžic & Bilandžija, 2009) which should join the Natura 2000 network when Croatia enters the European Union.
Molecular studies are currently ongoing at the Ruder Boškovic Institute that should shed light to intraspecific relations and the taxonomical status of certain populations (Bilandžija et al. 2009).
H. Bilandžija -
B. Jalžić -
Bilandžija, H., Patarcic, I., Podnar, M., Tvrtkovic, N., Cetkovic, H., 2009: Phylogenetic and phylogeographic analysis of endemic bivalve Congeria kusceri. Zbornik sažetaka 10. hrvatskog biološkog kongresa = Proceedings of Abstracts of 10th Croatian Biological Congress. Hrvatsko biološko društvo 1885, 179-180.
Bole, J., 1962: Congeria kusceri sp. n. (Bivalvia, Dreissenidae). Biol. vestnik 10, 55-61. Ljubljana.
Jalžic, B., 1998: The stygobiont bivalve Congeria kusceri Bole, 1962. (Bivalvia, Dreissenidae) in Croatia. Natura Croatica, Vol. 7. No. 4. 341-347, Zagreb.
Jalžic, B., 2001: The first finding of live stygobiont bivalve Congeria in Lika region, Croatia. Natura Croatica, Vol. 10. No. 3. 213-220. Zagreb.
Jalžic, B., Bilandžija, H., 2008: Znanstvena analiza podzemnih vrsta s Dodatka II Direktive o zaštiti prirodnih staništa i divlje faune i flore: Congeria kusceri. Interni izvještaj, Hrvatsko biospeleološko društvo, pp 6 + prilozi.
Jalžic, B., Bilandžija, H., 2009: Znanstvena analiza podzemnih vrsta s Dodatka II Direktive o zaštiti prirodnih staništa i divlje faune i flore: Congeria kusceri. Interni izvještaj, Hrvatsko biospeleološko društvo, pp 42 + prilozi.
Morton, B., Velkovrh, F., Sket, B., 1998: Biology and anatomy of the 'living fossil' Congeria kusceri (Bivalvia: Dreissenidae) from subterranean rivers and caves in the Dinaric karst of the former Yugoslavia. Journal of Zoology, 245, 147-174. London.