Melanopsis is a highly variable freshwater genus. We describe its systematics, distribution and extent of hybridization in the Jordan Valley. Our study is based upon conchiometrics of 760 snails, from 38 sites.
Three species are recognized: Snails with smooth shells (M. buccinoidea); with straight-ribbed shells in which the ribs extend almost the entire height of the ultimate whorl (costata); and with tubercle-ribbed shells in which the ribs usually extend about half the height of the ultimate whorl (saulcyi). Hybrids are found in zones of sympatry, both between buccinoidea and costata and between buccinoidea and saulcyi, at low frequencies and over distances of no more than a few hundred m.
Within costata we distinguish three groups, and tentatively suggest that they may be subspecies. Shells from the upper Jordan River are elongate (c. costata); those from Lake Kinneret are stout (c. jordanica); and in those of the Yarmouk each rib consists of a pronounced upper tubercule, fused to a pronounced, straight lower ridge (c. noetlingi). Within buccinoidea, shells from Nahal Dan differ in their shallow notch and small mouth-height.
The small, stout shell of c. jordanica correiates with a stormy habitat. A stout, globose shell could accommodate more foot muscle and thus enable a stronger adherence to rocks and boulders during severe storms.