ACTIVE MOVEMENTS AND OTHER ASPECTS OF THE BIOLOGY OF ASTICHOPUS AND LEPTOSYNAPTA (HOLOTHUROIDEA)

¹ Institute of Marine Biology, University of Puerto Rico, Mayaües, Puerto Rico

1. Aspects of the biology of the aspidochirotid, Astichopus multifidus and the apodid, Leptosynapta albicans, studied in Puerto Rico and California, respectively, were investigated in relation to the active movements performed by these species.

2. Astichopus is present in greatest abundance between 10 and 40 m. of depth on the northwestern coast of Puerto Rico. It often occurs in or near beds of the marine phanerogam, Halophila baillonis. Sandy beaches, cemented dunes, and beach rock, exposed to the heavy seas of the Atlantic Ocean, make up the shoreline of this region. Numerous large rivers loaded with terrigenous materials discharge on the north shore. The sediment on which Astichopus lives is comparatively fine-grained (median diameter = 0.212 mm.) and well sorted (_\g=fscr\= 1.1); the terrigenous component is high (62.5% ), calcareous bioclastic materials occur in substantial amounts (36.8%), and the organic matter content is low (0.7%). A smaller number of Astichopus has been collected from shallow water (1-3m.) in the winter, summer and autumn at La Parguera on the south coast.

3. In addition to a comparatively fast crawl, forward progression in Astichopus is executed by rapid walking and bounding movements, which in the latter case may approach a rate of 2 m./min. Rolling and exploratory movements are also performed by Astichopus.

4. Mechanical stimulation usually causes Astichopus to contract for 1-2 minutes. Walking, bounding and rolling movements are elicited by sudden changes in the temperature of the water, of the order of 3-4° C. A positive phototactic response occurs at low light intensities (5 foot-candles); phototaxis increases at higher light intensities, but no definite negative response is apparent. A strong positive attraction to red, green, blue and violet light is evident at a low intensity of 10 foot-candles. No clear tendencies were noted in geotactic or thigmotactic behavior. Bounding movements sometimes occurred when cucumbers were suddenly subjected to diluted sea water and oxygen-deficient water. Active movements were not evoked through the association of Astichopus with members of its own species or in the presence of other animals.

5. Coelomic fluids and alcohol extracts of the body wall of Astichopus are toxic to a variety of marine animals at concentrations of 1000-5000 ppm. It does not seem likely that a poison is released by the animal naturally, since the water in which active movements are performed is non-toxic and evisceration occurs only rarely.

6. Sinusoidal swimming movements were observed in adult Leptosymapta on three different occasions near the surface at night. Specimens subjected to a variety of experimental conditions in captivity failed to elicit the swimming response. Synaptula hydriformis, a related West Indian species, did not swim either when subjected to diverse stimuli as with Leptosynapta or when exposed to the juices of a presumed predatory trunk-fish.