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Rhogocytes of gastropod larvae are described from TEM images. These cells were found in the planktotrophic larvae of Amphissa columbiana, Trichotropis cancellata, Marsenina stearnsii (Caenogastropoda) and Nerita melanotragus (Neritimorpha) but not in Siphonaria denticulata (Heterobranchia). Previously these uniquely molluscan cells had been described in adult and direct developing larval gastropods only. Multiple functions have been proposed for rhogocytes, the most well supported being hemocyanin (HCN) synthesis. HCN was found within vacuoles of the rhogocytes of N. melanotragus but not within the caenogastropods. Caenogastropod rhogocytes may export HCN immediately after synthesis or they may synthesize a different protein product. Rhogocytes may be homologous with terminal cells of protonephridia, the latter used for excretion and osmoregulation. The presence of these two in gastropod larvae may be functionally related to larval body size. Large caenogastropod and neritimorph larvae have rhogocytes but not protonephridia, whereas the smaller heterobranch larvae have protonephridia but not rhogocytes. / Graduate

Most benthic marine invertebrates have long-lived planktonic ciliated larvae that must feed and grow to reach metamorphosis. Because ciliated cells in animals are unable to divide it is of considerable interest how ciliated larvae are able to grow. To understand how ciliated larvae grow I compared cell proliferation patterns in several species with planktotrophic larvae from five different phyla (Nemertea, Mollusca, Phoronida, Echinodermata, and Annelida). Cell proliferation events were detected using anti-phosphohistone antibody labeling, BrdU assays, and confocal microscopy. Studied larvae included some with monociliated epithelia (pluteus, bipinnaria, actinotroch, and mitraria) and others with multiciliated epithelia (metatrochophore, pilidium, and veliger). Dividing cells were detected in all studied larvae, but the pattern of dividing cells varied among types and correlated with the kind of epithelium (mono- vs. multiciliated) and phylogeny (e.g. protostome vs. deuterostome). Running z-projection movies of the actinotroch, mitraria, veliger and pilidium are included as supplemental files.