SANTAGATA, Scott; Smithsonian Marine Station: Evolutionary trends in the larval anatomy of the Bryozoa

Neuromuscular anatomy and the cytology of the presumptive juvenile tissues of cyclostomate and gymnolaemate bryozoan larvae were investigated with immunohistochemistry, cLSM, SEM, and TEM. Differences in the neuromuscular systems among systematic groups correlate with modifications of swimming and crawling orientations. Ctenostome bryozoans have diversified the size, shape, number, and cytological make-up of the swimming cells more than other morphological grades of bryozoans. Among all non-feeding larval types, there is also a functional relationship between body volume and the surface area of locomotory cilia. Despite anatomical differences, there are shared larval traits that are concordant with ‘super-family’ level groupings based on adult characters. Overall, the larval body of bryozoans consists of two regions that have been modified several times in terms of their larval function and their relative contributions to juvenile tissue. Considering the pre- and postrochal regions present in phyla with a trochophore larva and the larval body regions of other lophotrochozoans, it is plausible that a bipartite larval body is plesiomorphic for lophotrochozoans.