Meeting Abstract

P2.89  Sunday, Jan. 5 15:30  Comparative neuromuscular morphology of a scyphozoan and a staurozoan WESTLAKE, HE*; PAGE, LR; Univ. of Victoria; Univ. of Victoria hannahew@uvic.ca

The recent reclassification of Staurozoa as sister group to all other medusozoans upsets their classical interpretation as derived medusae with secondarily acquired stalked morphology. Their phylogenetic position suggests Stauromedusae are better interpreted as polyps that have developed novel medusoid features at their highly differentiated oral end. To identify stauromedusan neuromuscular features that are likely precursors of medusoid characters, we compared the stauromedusa Haliclystus “sanjuanensis” to polyps and ephyrae of the scyphozoan Aurelia aurita. Both species were treated with antibodies against FMRFamide, glutamate, taurine, and tyrosinated tubulin to label the nervous system and phalloidin to label the muscles. Haliclystus has both polypoid and medusoid neuromuscular features. Haliclystus and Aurelia ephyrae share a similar organization of manubrial muscles and both have a marginal circular muscle. The eight-part coronal muscle of Haliclystus is a possible homologue to the adult swimming muscle of Aurelia, but the coronal muscle of Haliclystus is composed entirely of smooth muscle whereas the swimming muscle of Aurelia is composed of both smooth and striated fibers. Polypoid features of Haliclystus include the four longitudinal muscle cords extending from pedal disc to tentacles. In Haliclystus these muscles are not innervated by FMRFamide-immunoreactive neurons as they are in Aurelia polyps. A single FMRFamide immunoreactive nerve net similar to the diffuse nerve net (DNN) of Aurelia polyps is present in Haliclystus, but the glutamate immunoreactive giant fiber nerve net (GFNN) of Aurelia ephyrae is absent. We conclude that precursors of novel medusoid musculature are more apparent in Haliclystus than precursors of novel medusoid neural characteristics.