Meeting Abstract

P2.134  Jan. 5  Neuromuscular Organization for the Polyp Tentacle of Aurelia YUAN, David*; NAKANISHI, Nagayasu; CAMARA, Anthony; JACOBS, David K.; UCLA; UCLA; UCLA; UCLA daveyuan@ucla.edu

Cnidarian tentacles are generally conceived of as having an ectodermal layer, an endodermal layer, and a medial lumen continuous with the gastrovascular cavity. However, polyp tentacles of some scyphozoans and hydrozoans are solid, with a single medial column of large vacuolated endodermal cells. These tentacles also contract rapidly and expand slowly. It has been argued previously that this pattern of extension and contraction was a consequence of the absence of circumferential muscles and that extension was a passive viscoelastic process. We have recently examined the Aurelia polyp tentacle in detail using stains such as sytox and phalloidin for nuclei and actin respectively, as well as antibodies to acetylated tubulin, FMRF, GnRH, and opsin in combination with confocal microscopy. These observations document the helically wound neural organization of FMRF positive sensory cells and neural filaments running the length of the tentacles. Furthermore, phalloidin staining reveals thin layer of actin fibers oriented in a circumferential direction inside the larger longitudinal muscle layer. Thus, contrary to previous interpretations there appears to be a circularly oriented contractile apparatus, albeit far smaller than the longitudinal muscle layer. Thus the dramatic elongation of these narrow tentacles is accommodated by what are very small circular muscles that are operating at a mechanical disadvantage-hence the slow extension. In addition, the pattern of contraction suggest that the vacuolated endodermal cells of the tentacles can operate as independent or partially independent hydrostats contracting “segments” of the tentacle.