Folia Historico-Naturalia Musei Matraensis - A Mátra Múzeum Természetrajzi Közleményei 9. (1984)
Kinzelbach, R. K.–Roth, G.: Patterns of distribution of some freshwater molluscs of the Levant region
2. A second group are the mainly costated or, rarely smooth shelled specimens which always possess a stepped outline. They occur in the Orontes river incl. Krasu and Afrin, the Quwaiq river, the Jordan river incl. Nähr az-Zarqä and at isolated localities of the Syrian Plateau. It is named M. pi. costata (OLIVIER, 1804); another distinct subspecies of the water boides of Palmyra is M. pi. obsolete (DAUTZENBERG, 1894). 3. The third group comprises individuals of the Euphrates river, probably representatives of a species of its own, Melanopsis nodosa FÉRUSSAC, 1823. Specimens of similar morphology are known from Pleistocene sites in the Orontes and Jordan valleys. These groups do apparently not represent local varieties or morphs but true genetic units, the status of which will have to be clarified in the future. The natural limis of distribution are frequently broken through by former or recent displacement. PALEOGOGRAPHICAL CONCLUSIONS The patterns of distribution even of he few species discussed here show principal agreement, hus their evolution may be explained by the same paleogeographical situations. These are in detail: 1. A north-south junction along the Levantine coast during the Pliocene or earlier, which allowed the spreading of Unio elongatulus eucinus, Leguminaia saulcyi, Potomida littoialis delesserti and L /ш'о tigridis (not treated here); the latter and L /ш'о elongatulus reached the Nile. 2. The particular development of the Levantine rift valley with the endemic species Dreissena bouiguignati and Vivipaius apameae, which are not treated here as well as the subspecies Potomida littoialis semiiugata and Unio teiminalis teiminalis. 3. A clear cut separation of the northern and southern part of the Levantine rift valley; connections existed only for a short period of time by way of the Biqâc plain (which was used as a pathway by Coibicula fluminalis) and the Damascus basin,- Maigaiitifeia homsensis and Unio teiminalis delicatus for instance are forms restricted to the northern part. 4. A connection between the northern Levantine rift valley and the Euphrates by way of the Quwaiq river and the Gabbűl basin during the Pliocene and perhaps even later; possibly also the Amik Gölü basin and the upper courses of Afrin and Karasu rivers discharged to the east; this was used by the genera Leguminaia, Potomida and Coibicula. 5. The present lower Orontes was formerly a short and unimportant river of the Mediterranean coastal plain which shares till now serveral faunal elements such as Potomida littoialis delesseiti, Leguminaia saulcyi, Unio elongatulus euciirus with the other coastal rivers. 6. The close junction between the lower course of the Orontes and the Ceyhan river during a period of marine regression during the Pleistocene, which led to a faunal exchange: Coibicula fluminalis and Melanopsis piaemoisa femssaci invaded the Ceyhan, the reverse way was used by Unio terminális, delicatus. 119
