CRUSTACEA. 
163 
bdella ) are often found attached to the walls of the branchial 
chamber. 
The number and variety of parasitic growths, both vegetable 
and animal, on the carapace of this form are remarkable. 
Balani of two species cover the back almost with a continuous 
rugose pile, adhering to the limbs, the abdomen, the foot-jaws, 
or each other. Coils of Serpulce and hard sandy tubes of 
Sabellaria interlace with these and fill up the depressions, and, 
with the former, occur on the tip of the abdomen as well as on 
less mobile situations. Fine tufts of Sertularia purriila and 
Crista eburnea adorn the surface of the carapace in others, or 
the parasitic algse thereon; while Halicliondria panicea forms 
a thick rugged crust, from which Balani , Serpulce , Anomice , 
zoophytes, and seaweeds emerge. Even the sockets of the 
eyes are invaded by the sponge. Moreover young examples 
are not unfrequently clothed with thick tufts of Obelia geni- 
culata. It would appear that it is not always on attaining 
full growth that moulting ceases for considerable intervals, 
since small specimens are found as completely covered with 
parasitic growths. In the rock-pools the carapace often forms 
a moving forest of seaweeds ; and in such specimens the shell 
is frequently fragile, so that the extraneous covering may be 
of use for protection, or else had grown with unusual rapidity, 
even before the carapace became fully consolidated. 
One old example had the internal antennas quite fixed by a 
hard sand-tube of Sabellaria ; and the young of the common 
mussel are occasionally found in the cavities for the eyes. 
In the young females the genital apertures are small, and 
the abdomen less developed; while in the adult the latter 
becomes hypertrophied, hollowed out on its ventral surface by 
the bending downwards of the outer edges, and touches the 
bases of the legs on each side. 
Hyas coarctatus , Leach; Bell, op. cit. p. 35. 
Common in deep water, and procured in hundreds amongst 
the coralline debris in the fishing-boats ; frequent in the 
stomachs of cod, haddock, and flounders. 
Y 
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