THE AUSTRALIAN MUSEUM MAGAZINE. 



245 



The Shell-dwelling Crab (Conchoecetes 

 artlficiosus) belies its name, for its associa- 

 tion with shells is purely for the sake of 

 disguise, and the creature is just as active, 

 or more so, when disengaged from such a 

 weighty covering. 



[Plioto.— G. C. Cliitton. 



This forms an adequate cloak to 

 protect and conceal the bearer, and is 

 firmly secured by a pair of nippers on 

 the hinder legs, which are very perfectly 

 developed, sharp and strong, and, like 

 those of the hand, are formed by the 

 opposition of the terminal joints to 

 prolongations of the last joints but one. 

 As its name implies, Conchoecetes is a 

 shell dweller, and there are several 

 species which practise this peculiar 

 mode of hiding. One can easily imagine 

 the surprise of the naturalist who first 

 discovered these peculiar crabs. The 

 appearance of shells apparently walking 

 along the shore must surely have tried 

 his conscience had he happened to have 

 been a little indulgent the night before. 

 By a wonderful arrangement of the 

 terminal joints of the second last pair of 

 legs, as previously described, Conchoe- 

 cetes is enabled to grasp the edge of 

 the single valve of a bivalve mollusc, 

 beneath which its presence when stat- 

 ionary Avould never be guessed. From 

 a downward view the only visible signs 

 of habitation are the two tiny terminal 

 claws of the prehensile hinder limbs 

 of the occupant, which overlap the 

 edge of the covering. One species 

 of the genus is fairly common in shallow 

 water at low tide on the sand and mud 



fiats of the north-east Australian coast, 

 whilst others are widely distributed 

 throughout the warmer seas of the 

 Indian and Pacific Oceans. 



Another near ally of the foregoing is 

 the Shaggy Oab {Drowidiojisis ex- 

 cavata), which invariably has a covering 

 of either sponge, or a more or less 

 bulky growth of a compound animal 

 colony belonging to the class of the 

 Ascidians. It is this latter covering 

 which seems to give camouflaged crabs 

 the most trouble. In many instances 

 the ascidian colony assumes such com- 

 jjaratively huge dimensions as to seem 

 more annoying than useful to the 

 bearer. The whole body of this species 

 is covered with a thick growth of coarse 

 hair, and the back is beautifully rounded 

 in shape. This fits comfortably into 

 the cavity of its protective covering, 

 giving the impression that the hole was 

 cut to the order of the occupant. 

 The species has a wide range along 



A Shaggy Crab (Dromidiopsis excavatai, 

 showing the relation of its size to the com- 

 paratively huge dimensions of a covering 

 consisting of a colony of compound ascidian. 

 The crab has been extracted from the cavity 

 it has created in its four-and-a-half inch 

 wide enveloping cloak. 



[riioto.— G. C. f'littoii. 



