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

waiq river and the Gabbül basin. Fossil records from the Jordan area are still to be confirmed. Until present the mussel in question was considered to be a subspecies of Potomida littoralis,, namely Potomida littoialis homsensis. According to MODELL (1964), however, this taxon belangs to the genus Maigaiitifeia; it is therefore considered here as a valid species, Margaiitifeia homsensis. During the Pliocene it spread from the lower Danube through the Vardar depression and the Egean lakes into the Orontes system. The closely related Margaritifera auricularia occurs in southwest and central European rivers. Because of its thick pink nacreous layers this shell served as jewelry since lang ago. A piece of shell was found near Polmyra. ro. Theodoxus jordani (SOWERBY, 1832) (Fig. 7}. Coming from the north, the Ponto-Caspian area, the ancestors of the widespread, quite polymorphic snail Theodoxus jordani penetrated into Middle East, where they are known to occur since the Pliocene (TCHERNOV, Г973). It has not yet been possible to establish clearly distinct subspecies. However, comparative studies on the radula teeth indicate a genetic heterogeneousness between different geographical units (ROTH, 1983), namely a) the southern part of the Levantine rift valley, where one out of two possible morphological types of the first lateral tooth, the „J-form" predominates (with exception of the springs arround the Dead Sea), b) the coastal rivers except for the Nahr al-Kabïr (N), where solely the second type, the „A-form" occurs, and a) the southern part of the Levantine rift valley, where one out of two gether. It is not very easy to explain this varying but orderly distribution of radula types within the populations. Probably the A-form represents a generally distributed original state. On the other hand, the J-form may have developed in an isolated population, most likely in the area of the Jordan valley, and later invaded the Orontes system and the Euphrates. This would at least help to explain its absence from the coastal rivers. n. Melanopsis praemorsa (L., 1758) (Fig. 8). In this context only a few principal features of the subspecific arrangement of the snail Melanopsis praemorsa can be outlined. The basic pattern of distribution, which is exhibited by the mussels, applies in this case as well despite quite different means of dispersal. 1. The first group consists of mainly smooth shelled or, rarely finely ribbed specimens without shouldered whorls. It is distributed in Anatolia, in the tributaries to the upper Euphrates and the,coastal rivers of the Levant region. It reaches the Quwaiq river and Gabül basin, the Damascus basin, the Biqâc plain and parts of the Jordan system. It may be subdivided into the chiefly black Melanopsis, praemorsa ferussaci (ROTH, 1839) of the Levantine coast and Palestine and the yellowish or ochre coloured M. pr. olivieri (BOURGUIGNAT, 1884) of eastern Anatolia. 118