| (Caption) MARINE SNAIL, Hermissenda crassicornis, pictured in a seawater aquarium in this photograph made by Pierre A. Henkart of the National Cancer Institute, is about an inch and a half long. The two large oral tentacles are tactile and chemosensory organs; the smaller dorsal tentacles called rhinophores are thought to sense water movement. The animal's central nervous system is on the buccal crest just behind the rhinophores. The plumelike appendage covering the snail's back, the cerata, may serve, like gills, as gas-exchange organs. |
