The shallow-water Rissoidae (Mollusca, Gastropoda) of the Azores and some aspects of their ecology

A critical review of the distribution of the Rissoidae on the islands of the Azorean Archipelago is made, on the basis of bibliographic data as well as newly-collected samples. Twenty three taxa of Rissoidae are given to the Azores: twelve endemic species, three restricted to the Azores and Madeira/Selvagens archipelago and two with wider distribution. Of the remaining taxa, one is an unidentified species of Setia and five are records not confirmed by this study. The assemblage of Rissoidae associated with heterogeneous algae on a rocky shore on the northern coast of São Miguel Island, Azores, is also described. Aspects of community structure (species composition, abundance and zonation) were studied and a multispecies analysis conducted using clustering techniques. Some comments are also made regarding the Rissoidae speciation that has occurred in the Azores and its relation to the main sea-surface circulation in this area of the Atlantic Ocean.