THE RELEASE OF THE PEDAL DISK IN AN UNDESCRIBED SPECIES OF TEALIA (ANTHOZOA: ACTINIARIA)

¹ Bamfield Marine Station, Bamfield, British Columbia, Canada V0R 1B0
² Department of Zoology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9

Specimens presumed to belong to an undescribed species of Tealia were collected subtidally in the northeast Pacific. In contact with the asteroids Dermasterias imbricata and Patiria miniata, these animals expanded their oral disks, constricted their columns, and detached their pedal disks. Other asteroids had no such effect. Of five other species of Tealia, only T. piscivora showed similar behavior and only to D. imbricata. Electrophysiological records showed: 1) that D. imbricata evokes pulses in a slow conduction system (McFarlane's SS1); and 2) that a train of electrical stimuli also causes SS1 pulses and brings about the release. It is concluded that SS1 pulses trigger the releasing behavior of Tealia sp. as they do the release and swimming behavior of Stomphia spp. A review of pedal disk release in the actinians shows that it occurs only in certain genera and species in several families not closely related. Although the circumstances and functions of the release where known are not the same in different species, the neurophysiological mechanisms employed are strikingly similar. Also discussed are the active role of the pedal disk in special behavior patterns and a possible function of the release in the escape of Tealia sp. from a predator.