PREY-PREDATOR RECOGNITION 39 



sence of chemoreception, can also be used by these animals. If they can 

 differentiate, by touch alone, bivalves or barnacle shell from a rough rock, 

 this would seem to imply a fair degree of central integration or very specific 

 sense receptors. On the other hand, these animals may be able to find their 

 prey from the relatively low concentrations of waste products that are being 

 excreted into the water, although this would imply that they possess the 

 degree of sensitivity and selectivity that appears to characterize many sym- 

 bionts (Davenport, 1955). It would seem most unlikely that such stimuli 

 as were used by Copeland (extracts of fish and oyster meat) would be the 

 naturally attracting substances for the gastropods which feed on live bi- 

 valves, or such forms as Scaphander which swallow whole prey (Hunt, 

 1925). 



The best known cases of escape reactions among the invertebrates to be 

 be considered here involve the reactions of certain moUusks in the presence 

 of starfish (Bullock, 1953, for review). Nassa, which is probably more of 

 a scavenger than a carnivore restricted to living prey, shows a classic and 

 peculiar leaping withdrawal when touched by certain starfish. While this 

 example has not yet been sufficiently analyzed to preclude a role of tactile 

 stimulation of the snail by the predator's tube feet (compare Dakin, 1910, 

 and Hoffmann, 1930) , it seems quite certain that strong chemo-stimulation 

 by substances on the surface of the echinoderm are the primary cue. Re- 

 cently Heinsohn ( 1955 ) , looking at this response, reported a violent twist- 

 ing, followed by rapid locomotion, by the snail Caliostoma responding to an 

 extract of Pisaster. The total response lasted at least 30 minutes, during 

 which time the animal moved over 1.6 meters. Interestingly enough, there 

 seems good reason to suppose that other groups of animals are equally 

 sensitive to substances on the integument of certain starfishes. Hancock 

 (1955) mentions the toxicity of Solaster, while I have observed what may 

 be the same response in several species of ophiuroids to Solaster and Derm- 

 asterias. The latter star is particularly effective in causing the extraordi- 

 nary escape response of the sea anemone Stomphia, to be mentioned later. 



While this relative wealth of information is available concerning possible 

 recognition and escape reactions of gastropods to starfish, apparently 

 nothing is known about similar behavior initiated by cues from fish ; yet it 

 would seem (Hunt, 1925) that a variety of bottom fish form the chief 

 predators of these snails. Clearly, however, the general pattern of gastro- 

 pod activities — movement away from well-lit areas for some species, or 

 crowding into the intertidal or even supratidal zones, the occupancy of 

 crevices, and so forth — all tend to aid these mollusks in avoiding their 

 enemies. 



Two complicating factors in any physiological analysis of behavior are 

 the possibilities that conditioning may occur or that changing "physio- 



