Rhogocytes in larval gastropods

Abstract

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.