SOME COMMENSALS OF INDIAN ALCYON ARIANS. 
933 
shell with fragments of seaweed, but occasionally I have met with individuals 
that have improved on this, hy camouflaging the carapace and limbs with many 
worm-like Synaptids, striped very distinctively purple and white {Synapta 
striata). These live normally as commensals with certain rough-surfaced sjwnges ; 
it is evident that the crab picks these off the sponge and transfers them to its 
own back and limbs. (Fig. 3.) The drawing given has been made from a preserved 
Fig 3. — A Spider-crab (Halimus) from Palk Bay that has decorated 
its carapace and limbs with striped Sjniaptids for protec- 
tion. (Original.) 
specimen, after several synaptse nad been removed, but even so, it shows 
how symmetrically the synaptse are arranged, and particularly the way in 
which each leg of the crab has its own synapta, arranged so as to conceal it 
effectually. In addition to concealing the crab, the S3maptte give it protection 
through their warning colouration ; their skin is full of tiny calcareous spicules 
of which many are in the form of ‘anchors’, the points (flukes) projecting, so 
that if touched the synapta adheres like a burr and is not easily shaken off. 
Except in regard to the association of one species of Dromia with Spongodes as 
above detailed, I have little to add to what is known of the masking habits of 
the velvet-crabs. Most usually a massive silicious sponge is used to hide the 
body, as shown in figure i. In this case the sponge has been so long held 
in position, that its growth has gone on to such an extent that it fits the body 
of the crab like a glove, indeed the crab appears to be occupying merely a cavity 
scooped out in the underside of a massive ball of sponge. Less frequently an 
ascidian colony is utihzed and on one occasion I noted that -the concealing 
cloak carried by a tiny Dromia, only a quarter of an inch across the carapace. 
