PREDATOR RECOGNITION AND ESCAPE RESPONSES OF SOME INTERTIDAL GASTROPODS IN PRESENCE OF STARFISH by THEODORE HOLMES BULLOCK (Department of Zoology, University of California, Los Angeles) (Rec. 12-1-1953) Specific, adaptive behavior of prey species indicating recognition of pre- dator is known for a very limited list of invertebrates. Defensive adaptations of many types are described, but these are commonly structural or non- specific in respect of foreign species. The limited knowledge of specific escape responses does not permit the conclusion that such behavior is in fact rare among lower groups. It seems of some general interest, therefore, when such behavior comes to light among a number of the most familiar and abundant intertidal species. It has been known for many years that species of sand flat snails of the genus Nassarius (= Nassa auct.) leap away from starfish in a peculiar manner (BAUER, 1913; WEBER, 1924; HOFFMANN, 1930) and that scallops of the genus Pecten swim in a manner differing from their usual locomotion upon contact with, supposedly, a secretion from the skin of starfish (DAKIN, 1910; BAUER, 1912, 1913). These cases are so much more striking, rapidly and clearly responding than those in the present report that they are the material of preference for more detailed study of the mechanism of stimu- lation. HOFFMANN (1930) has made a significant beginning on this problem. Fresh water snails (Physa) are known to retreat abruptly from contact with certain leeches (Glossosiphonia) (DEGNER, IC)2I ; WREDE, 1928). Echinoids show defensive responses apparently specific t7o'starfish. Thus PROUIIO ( I89o) desoribed the special type of reaction of a sea urchin to these predators, the spines being deflected away from the point of attack to uncover the short but effective gemmiform pedicellariae. Sand dollars of the species Dendraster excentricus (Eschscholtz) sink into the sand in a period of a few minutes when the starfish Pisaster brevispinus (Stimpson) 131 is placed on a bed of the echinoids. The response extends to individuals several centimeters from the asteroid (MACGINITIE and MACGINITIE, 1949). The present study grew out of an observation (HADERLIE, 1947) which was at first the more incredible because it dealt with hitherto undescribed but conspicuous behavior of the commonest limpets. Inquiry among some of the best naturalists has revealed that this behavior was indeed unknown to them. Several students have made confirmatory studies, in particular FEDER All to be (1948). details reported here, however, have been observed directly by the writer, unless specifically indicated otherwise. MATERIALS AND METHODS were Simple experiments conducted in the field and in the aquarium. They will become clear in the description of results. The species used are listed below. Indentifications are not authoritative, but in most cases there is no similar species with which that listed can be confused in this area. GASTROPODA Acmaea digitalis Eschscholtz Lottia gigantea Sowerby A. scabra (Gould) Fissurella volcano Reeve A. cassis Esch. A. (= pelta Esch.) Megathura crenulata (Sowerby) A. fenestrata (Reeve) Haliotis cracherodii Leach A. limatula Carpenter Tegula funebralis (Adams) A. scutuwc Esch. T. brunnea (Philippi) A. insessa (Hinds) T. ligulata (Menke) Littorina planaxis Philippi Norrisia norrisii (Sowerby) L. scutulata Gould Zonaria spadicea (Swainson) Nassarius fossata (Gould) Acanthinca spirata Blainville ECHINODERMATA Asteroidea Holothuroidea Pisaster ochraceus (Brandt) Stichopus californicus (Stimpson) P. giganteus (Stimpson) P. brevispinus (Stimpson) Patiria miniata (Brandt) Leptasterias aequalis (Stimpson) Echinoidea Heyzricia leviuscula (Stimpson) Astrometis sertulifera (Xantus) Strongylocentrotus purpuratus Pycnopodia helianthoides (Brandt) (Stimpson) All of these species are from the intertidal of central or of southern California. .