Late Cretaceous to ?Paleocene freshwater, brackish-water and marine molluscs from Al-Khodh, Oman

Bivalvia and Gastropoda from the late Campanian to Maastrichtian deltaic Al-Khodh Formation and from the overlying ?Paleocene shallow marine Jafnayn Limestone Formation of northeastern Oman are described. Freshwater bivalves include three species of Unionidae, left in open nomenclature, due to limited preservation. These are the first pre-Pleistocene unionids recorded from the Arabian Peninsula, where large freshwater bivalves are absent today. Brackish-water bivalves are represented by two species of Cyrenidae. Geloina amithoscutana sp. nov. extends the range of Geloina to the Mesozoic and to ancient Africa. Muscatella biszczukae gen. et sp. nov. has a unique combination of characters not shared with other genera in the Cyrenidae. Brackish-water gastropods comprise Stephaniphera coronata gen. et sp. nov. in the Hemisinidae; Subtemenia morgani in the new genus Subtemenia (Pseudomelaniidae); Cosinia sp. (Thiaridae); Pyrazus sp. (Batillariidae); and Ringiculidae sp. indet. From the Jafnayn Limestone Formation, several marginal marine mollusc taxa are also reported. The fossils are assigned to four mollusc communities and associations, which are indicative of different salinity regimes.