MARINE CRUSTACEANS. 
PARTS X. AND XI 
By L. A. BorrapatLe, M.A., Lecturer in Natural Sciences at Selwyn 
College, Cambridge. 
(With Plates XLVII. and XLVIII. and Text-figures 122—6.) 
X. THE SPIDER-CRABS (OXYRHYNCHA). 
THE Oxyrhyncha are a fairly well characterized group. Sharply separated, on the one 
hand from the Dromiacea by the coxal opening of the oviduct, the loss of the first 
abdominal limb in the female, and the normal shape and position of the last pair of legs 
(except in two or three cases as Ocinopus (Fig. 123), Grypachaeus and Zebrida), and on 
the other hand from the Oxystomata by the square mouth and the normal maxillipeds 
(Pl. XLVII. fig. 5b), they differ from the Brachyrhyncha in the shape of the body, which 
is narrowed in the fore part, so that in most cases it is triangular, and has a well-marked 
rostrum (Pl. XLVII., and Text-figs. 122 and 123), and usually in the imperfection of the orbits. 
Slender legs and weak chelae are another common feature, but not a diagnostic one. Their 
prevailing habitat may be summed up by saying that they are the crabs of the weed and 
weed-like animals, but this statement needs some explanation and qualification. 
The loss of their tail-fin has left the crabs, as a whole, a distinctly slower-moving 
group than most of the tailed Reptantia. To this there are, indeed, exceptions—as, for 
instance, the Ocypodes on land and the swimming crabs in the water—but for the bulk 
of the Brachyura it holds good, and each of the sections of the tribe has had to meet 
the difficulty in its own way. In the Brachyrhyncha the cuticle has generally become 
thickened into a stout armour, while the crab keeps fairly active in its habits, at all events 
after dusk, and usually defends itself vigorously with its strong chelae when it is attacked. 
In this legion protective coloration and shape are comparatively rare, and the habit of 
covering the body with foreign objects decidedly so (Caphyra), though the custom of hiding 
under stones is common. The remaining groups have, so to say, accepted the situation. 
Driven by the loss of their tail-fin to lead a sluggish life, they have found safety in 
exaggerating this inertness and combining it with various devices for escaping observation. 
The Dromiacea hold foreign bodies over their backs with their hind legs, the Oxystomes 
bury themselves in sand or shingle, and in each of these groups the most characteristic 
features, to which they owe their distinctness, are due to the method of concealment’. The 
1 See above, p. 434, 
