THE AUSTRALIAN MUSEUM MAGAZINE. 



243 



Crustacean Camoufleurs, 



By Frank A. McNeill. 



CAMOUFLAGE is a term which 

 has only recently come into 

 almost universal usage. It had 

 its origin many years ago in France 

 and, before the days of the World War, 

 stood for the art practised by the people 

 of that country in producing artistic 

 but deceptive screen effects on the 

 legitimate stage. On the outbreak of 

 hostilities a new use was found for 

 camouflage, and the term was ex- 

 panded to embody all those well- 

 known and elaborate measures adop- 

 ted by the various belligerents for the 

 protective colouring, screening, and 

 covering of vital objects both in attack 

 and defence. Just as the art has been 

 developed by man, so do we find many 

 parallel instances of its use among 

 some of nature's more lowly organised 

 children. 



Mother Nature has paid particular 

 attention to the crabs, for example, 

 and many of them are endowed with 

 wonderful modifications of structure 

 which enable them to escape the notice 

 of their enemies or creep unobserved 

 upon Iheir prey. 



Many of the Spider Crabs are re- 

 markably clever and proficient in their 

 methods of disguise, and as a conse- 

 quence are usually very sluggish in 

 their movements. One of the common 

 Australian representatives of this group 

 of crabs is a species known as Hyastenus 

 diamnthus, commonly called the Sponge 

 Crab. It has a wide range along our 

 eastern shores, occurring very plenti- 

 fully in the bays and estuaries, and is 

 very common in Port Jackson, where 

 it frequently inhabits water over muddy 

 bottoms. When captured, it is in- 

 variably found to be almost completely 

 hidden under a luxuriant growth of 

 marine life, principally various types 

 of sponges. On close examination, it 

 will be seen that the attachment of the 

 disguise to its back and legs is effected 

 by means of numerous, stout, hooked 



hairs, which are embedded in the sub- 

 stance of the hard shell. But if an ex- 

 ample of the species were secured imme- 

 diately after it had cast its shell, as it 

 must often do, it would be found to be 

 covered with a thick coat of these hairs : 

 and their tips, instead of being curled 

 over, would be seen to be almost 

 straight. With the hardening process 

 which takes place, these tips, like the 

 tendrils of a vine, soon begin to curl 

 and twine around the stems of marine 

 growths placed in position l)y the crab. 



The Sponge Crab (Hyastenus diacanthus), 

 with half of the body denuded of hairs and 

 protective covering. One has only to block 

 out this bared portion to obtain an impression 

 of the shapeless appearance which the 

 creature assumes in life. 



[Photo. — G. C. Clutton. 



With protective covering such as this 

 the Sponge Crab is practically immune 

 from attack as it lies huddled-up on the 

 bottom, and the same tactics ensure it 

 a meal when hungry if practised on an 

 unwary prey. The animals which pro- 

 vide the cloak, however, are apt to grow 

 if uncontrolled, and envelop their 

 bearer — a contingency doubtless over- 

 come by the crab pruning off superfluous 

 portions. This would undoubtedly be 



