COLOR POLYMORPHISM IN THE MANGROVE SNAIL LITTORARIA-INTERMEDIA IN SINAI

Samples of Littoraria intermedia Philippi (Gastropoda: Littorinidae) h ave been examined from an isolated mangrove at the southern end of the Sinai Peninsula, Egypt. The snails are abundant on the lower trunks a nd pneumatophores of Avicennia marina. Littoraria intermedia is usuall y monomorphic in shell colour, but here it is polymorphic. There is an orange morph, similar to the orange morph of leaf-living Littoraria s pecies, at a frequency of about 8%, and there may also be distinct mor phs in the dark class. The trunk substratum also shows distinct patche s of brown and black colour. A substantial amount of predation by crab s is inferred from the observed frequency of shell breakage. Polymorph ism may therefore occur in species of Littoraria in populations subjec t to predation. It is not, as has been suggested, restricted to situat ions where predation may be assumed to be negligible.