A COMPARATIVE-STUDY OF THE FUNCTIONAL-MORPHOLOGY OF SEMELE PURPURASCENS (GMELIN, 1791) AND SEMELE PROFICUA (PULTENEY, 1799) (BIVALVIA, SEMELIDAE)

A comparative study of the functional morphology of Semele purpurascen s (Gmelin, 1791) and Semele proficua (Pulteney, 1799), correlated with the habit and mode of life of both species, was made. Special attenti on was paid to the siphons, mantle, organs of the pallial cavity, musc ulature, and alimentary canal. Both species have a mosaic of morpholog ical and ecological aspects, some typical of specialized suspension fe eders, others of the deposit-feeding tellinaceans. The behavior of the siphons, the morphology and sorting devices of the organs in the pall ial cavity, and the stomach contents reveal a non-selective suspension -feeding habit. According to the most recent view of evolution within the Tellinacea, S. purpurascens and S. proficua might be classified as representatives of the group considered intermediate in the evolution ary line that proceeds from an early selective suspension-feeding ance stor to the modern and exclusively deposit-feeding Tellinacea. Details of the organization of the siphonal retractors of a representative of the Tellinacea are given for the first time; the controversy regardin g the occurrence of pedal elevator muscles in Semele is also discussed . Their presence in the genus is confirmed, although they are more wea kly developed and functionally inoperative than those of fast-burrowin g Tellinacea.