Meeting Abstract

P1.132  Tuesday, Jan. 4  Role of the Frenula in Cubomedusan Directional Swimming EICHINGER, Justin M*; SATTERLIE, Richard A; University of North Carolina Wilmington; University of North Carolina Wilmington jme1463@uncw.edu

Box Jellyfish (Class: Cubozoa) are strong, active swimmers capable of evading hazardous obstacles and orienting to photic stimuli. However, the underlying neuromuscular physiology responsible for complex swimming behaviors requires further investigation. Currently, turning is accompanied by asymmetrical deformations of the velarium, a striated muscle sheet encircling the bell opening. Radial, buttress-like muscles, termed frenula, are presently thought to serve only a stabilizing structural role during swimming. We hypothesize they may serve a greater function in cubomedusan turning behavior than previously thought. Investigations using confocal-light and electron microscopy as well as dissected and whole-animal swimming experiments were used to assess the control of turning in cubomedusae. During a turning event, frenular contractions in the radial axis result in shortening of the bell height as the velarium is retracted upward towards the bell apex. This retraction enables directional fluid ejection from the bell opening and hence culminates in a turn by the swimming medusa. Free-swimming cubomedusae lost functional turning ability after “disconnecting” neurons of the frenula from the rest of the motor nerve net. The frenulum is the most densely-innervated swim muscle in representative medusae from two cubozoan families (Carybdeidae; Tripedaliidae), followed by the velarium and subumbrella. The frenular nerve net has a distinct radial orientation in parallel with muscle cell orientation, whereas neurons in the other two regions of circularly-oriented swim muscle are distributed more randomly in non-directional networks. Our data suggest the frenula are important components in producing asymmetric velarial contractions to produce turning in cubomedusae.