Meeting Abstract

P3.73  Jan. 6  Muscular organization of the rhopalial stalk in Cubomedusae (Cnidaria) JACOBSON, B.R.*; SATTERLIE, R.A.; University of North Carolina, Wilmington; University of North Carolina, Wilmington brj0035@uncw.edu

Cnidarians have long held our attention in the scientific world, but we know little about the structure and formation of sensory structures of the motile forms, jellyfish. Cubomedusae, or box jellyfish, were once classified as Scyphomedusa but recent evidence suggests they deserve class status. Box jellyfish have four sophisticated sensory structures, or rhopalia, one on each side of the box-shaped bell. Each rhopalium contains a statolith, two complex eyes, four ocelli and sensory epithelia. Each rhopalium is suspended by a stalk within a cavity (niche) that opens on the outside of the bell. Muscle in the stalk may aid in moving the rhopalium behind a �hood,� exumbrellar tissue that partially covers the opening to the rhopalial niche. The muscle in the rhopalial stalk is ectodermal, longitudinal, and asymmetric. One function of the stalk musculature is to pull the rhopalium inward (orally) to shield the rhopalia from harm. Active muscular control of the rhopalia has been noted in Carybdea sivickisi, suggesting that the stalk musculature may aid vision by turning the rhopalium as the animal moves. In Carybdea marsupialis, however, muscle in the stalk is found only in the oral side. Four species of box jellyfish, including Carybdea marsupialis (Cnidaria: Cubozoa) are compared to determine the function and morphology of the rhopalial stalk with an emphasis on the muscular organization.