Habits, Reactions, and Associations in Ocypoda arenaria. 33 



Ocypoda is not able to live very long without water, although it may 

 stay down in its damp, cool burrow for several hours. When in the direct 

 sunlight without water it lives but a short time. Of 10 specimens placed 

 in the sun in a wooden tub all but 3 had died after 4 hours' exposure. 

 Other specimens kept in a dry aquarium in the laboratory and not exposed 

 to the direct sunlight lived almost 24 hours. Although Ocypoda can live 

 probably not over 24 hours in a dry place, it remains alive much longer in 

 damp sand. Several specimens placed in an aquarium and buried to a 

 depth of 15 inches in damp sand were alive and active at the end of 48 

 hours. 



ENEMIES, DEFENSE, HIDING, SLEEPING, ETC. 



On Loggerhead Key, Ocypoda does not have many enemies. The gray 

 snapper and man seem to be the only large animals that molest them, but 

 they are undoubtedly troubled by parasites and sometimes they are killed by 

 their own kind. The writer has often seen gray snappers darting about close 

 to the beach when an ocypoda has been driven into the water. As a rule 

 the latter keeps just out of reach, but occasionally a young one will be 

 snapped up by the fish. The large adults defend themselves fairly well 

 when dropped into deep water among a number of snappers. Upon the ap- 

 proach of the fish the crab strikes out with its large chela in the same way 

 that it does on land and this usually drives the gray snapper away. Eventu- 

 ally, however, if it does not crawl into shallow water its ambulatory ap- 

 pendages are bitten off one by one and the body is torn to pieces. Such 

 observations can be easily made at Loggerhead Key, because the water is 

 very clear. 



Bethe (1897) has described what he calls the " Aufbaum Reflex" of 

 Carcimis vianas. This attitude, he tells us, is brought about by stroking 

 along the back or head and also by moving an object in front of the crab. 

 In the case of Ocypoda a similar attitude is assumed and it is undoubtedly 

 one of defense. The crab rises up on the distal segments of its walking 

 legs, the chelae are raised and spread for apart and the body proper is held 

 well up above the surface of the sand. This defensive attitude is shown in 

 plate I, fig. c. 



As a rule, when Ocypoda is disturbed by man it either runs into its bur- 

 row or, when hard-pressed, goes into the water; but this interesting crab 

 has another way of concealing itself from man. Occasionally an individual 

 is seen which, instead of trying to find a burrow or attempting to run into 

 the water, will settle down in some little hollow, push its body backward 

 into the sand, and then with its posterior ambulatory appendages throw sand 

 over itself until most of the body is covered. Usually the eyes remain per- 

 pendicular, but sometimes they are dropped into their sockets. 



Another condition in which Ocypoda is occasionally found is the resting 

 or " sleeping " condition. I have seen a few individuals in this state during 



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