My research tested hypotheses about the evolutionary origin of a novel feature by modification of development. The novelty is the growing larval shell of gastropod molluscs, which emerged when gastropod larvae acquired the ability to feed. One hypothesis states that the growing larval shell in the Heterobranchia is a continuation of the embryonic phase of shell secretion. The second hypothesis states that the larval shell in the Caenogastropoda may be a precocious juvenile shell. These hypotheses implicate heterochrony. To test these hypotheses, I examined ultrastructural features of the shell-secreting cells of two or three life history stages in a member of each of four clades of gastropods: the Patellogastropoda, Vetigastropoda, Caenogastropoda, and Heterobranchia. My results are consistent with the first hypothesis, but I found no ultrastructural support for the second hypothesis. These results provide the most comprehensive comparative data set on the ontogeny of shell-secreting cells for the Gastropoda. / Graduate / 0433

Foi estudada a morfologia externa e interna de Calliostoma adspersum, C. depictum e C. hassler, procedentes da costa brasileira. Tegula viridula também foi estudada como parâmetro comparativo externo. Foi possível averiguar características anatômicas que diferenciam todas as espécies entre si. Diferenças significativas foram encontradas principalmente nas seguintes estruturas: concha; coloração e papilas do pé; musculatura do odontóforo; esôfago anterior; estômago; ceco em espiral e alça intestinal. Calliostoma, de acordo com dados preliminares, diferencia-se dos demais troquídeos por apresentar: redução ou perda dos lobos cefálicos; pseudoprobóscide; presença de ampola renal; uma alça intestinal fora da hemocela e o músculo m1d do odontóforo. / The external and internal morphology of Calliostoma adspersum, C. depictum and C. hassler, from Brazilian coast, was studied. Tegula viridula was also analyzed as outgroup. Anatomical characteristics that differentiate all species were found. The major differences were found mainly in the structures: shell; color and papillaes foot; odontophore musculature; anterior esophagus; stomach; spiral caecum and intestinal looping. Calliostoma, according to preliminary data, differentiates from other Trochidae in presenting: reduction or lost of cephalic lappets; pseudoproboscid; renal ampolla; intestinal looping outside haemocoel and m1d odontophore muscle

Foi estudada a morfologia externa e interna de Calliostoma adspersum, C. depictum e C. hassler, procedentes da costa brasileira. Tegula viridula também foi estudada como parâmetro comparativo externo. Foi possível averiguar características anatômicas que diferenciam todas as espécies entre si. Diferenças significativas foram encontradas principalmente nas seguintes estruturas: concha; coloração e papilas do pé; musculatura do odontóforo; esôfago anterior; estômago; ceco em espiral e alça intestinal. Calliostoma, de acordo com dados preliminares, diferencia-se dos demais troquídeos por apresentar: redução ou perda dos lobos cefálicos; pseudoprobóscide; presença de ampola renal; uma alça intestinal fora da hemocela e o músculo m1d do odontóforo. / The external and internal morphology of Calliostoma adspersum, C. depictum and C. hassler, from Brazilian coast, was studied. Tegula viridula was also analyzed as outgroup. Anatomical characteristics that differentiate all species were found. The major differences were found mainly in the structures: shell; color and papillaes foot; odontophore musculature; anterior esophagus; stomach; spiral caecum and intestinal looping. Calliostoma, according to preliminary data, differentiates from other Trochidae in presenting: reduction or lost of cephalic lappets; pseudoproboscid; renal ampolla; intestinal looping outside haemocoel and m1d odontophore muscle