Meeting Abstract

P3.82  Friday, Jan. 6  Confocal microscopy study of embryonic development in the viviparous hoplonemertean Prosorhochmus americanus. SPINDLE, ST*; TURBEVILLE, JM; Virginia Commonwealth University; Virginia Commonwealth University

Recent studies of hoplonenemertean planktonic and encapsulated planuliform larvae have greatly clarified their development and provided insight into larval evolution within the phylum. However, an assessment of viviparous development using modern techniques is lacking. To help facilitate a comprehensive comparative evaluation of developmental diversity within hoplonemerteans, we have initiated a confocal laser scanning microscopy investigation of the development in Prosorhochmus americanus, one of the few nemertean species that is both hermaphroditic and viviparous. Phalloidin staining reveals that the foregut, midgut, proboscis and body wall musculature form early in development. These results are consistent with those for planktonic hoplonemertean larvae. The cerebral organs form from paired invaginations situated near the anterior end of the embryo as described for some hoplonemertean planuliform larvae. Acetylated tubulin antibody labeling shows that late stage embryos are uniformly ciliated, and in some specimens a caudal ciliary cirrus is present, which is characteristic of species with planktonic larvae. The caudal cirrus may be interpreted as a vestigial structure in the non-swimming P. americanus embryos. Our preliminary observations provide no evidence for a transitory larval epidermis during the development of this species, but analysis of additional stages will be necessary to verify its absence. Analysis of the development of the nervous system in this species is ongoing, and both phalloidin staining and acetylated tubulin antibody labeling indicate that the cerebral ganglia and lateral nerve cords are present in early-stage embryos.