Field studies on the north coast of Papua New Guinea show that there are three species in the Littorina scabra complex on mangroves. Two are restricted to root structures, while the third occurs on the leaves. The species differ in shell shape, ornamentation and colour, in penis shape, and in radula morphology. The shells of the leaf species are much weaker than those from the roots. Many of the differences observed may be adaptive on the preferred substratum.