THE ETHOLOGY OF THE SYNAPTID HOLOTHURIAN, OPHEODESOMA SPECTABILIS

Abstract

Opheodesoma spectabilis commonly occurs in aggregations in the alga Sargassum echinocarpus, a source of shade from which it scrapes adhering detritus, and which allows the dense populations necessary for efficient spawning. The animal is photonegative and moves away from a strong light source. Ocelli provide information on the direction and intensity of sunlight. Statocysts, aided by tactile sensitivity, maintain dorsoventral equilibrium."They may also inhibit unwarranted rapid locomotion. The animal shows no gravity orientation. All sensory receptors are most concentrated in the region of the tentacle crown, and their interaction in controlling the animal's reactions implies considerable central integration of stimuli. The three primary muscular activities are the rhythmic contraction and extension of the tentacles, used in feeding and for slow locomotion; peristalsis of the body wall, involved in rapid locomotion; and the contraction, bending, and reextension of the anterior portion of the body. These activities may vary in rate and amplitude and occur independently or in any combinations. Their initiation and coordination are under central nervous control. Opheodesoma spectabilis has a diurnal rhythm of behavior, reaching an activity peak during the early evening hours and apparently directly dependent on changes in light intensity. Spawning occurs during the summer months.