Decapoda — Br achy lira, Crabs. 
65 
The Dromiacea or Sponge- Crabs are the most primitive of the Table-case 
existing Brachyura. The last pair, or the last two pairs, of legs are No ’ 12 ' 
dorsal in position, with hooked or prehensile claws, and are used 
for holding a piece of sponge, an Ascidian, or half of a bivalve 
shell, under which the animal is completely hidden. The mouth- 
frame is square. The primitive character of the group is shown 
especially by the retention of a vestigial pair of limbs on the first 
abdominal somite of the female, and ; often on the sixth abdominal 
Fig. 44. 
Dromia vulgaris. Front view of a specimen carrying on its back a mass of the 
sponge Clionc celata (reduced). [Table-case No. 12.] 
somite in both sexes ( sec the exhibited specimen of Dromia laior'). 
The basal segment of the antenna is large and unusually free, 
the pits into which the antennules fold are not separated from the 
orbits, and the gills are, in most cases, more numerous than in the 
other Brachyura. The oviducts of the female open on the first 
segment of the third pair of legs. 
Many of the Dromiacea, especially the more primitive forms, 
inhabit the deep sea. Dromia vulgaris (Fig. 44), which occurs off 
the South of England, belongs to the family Drorniiclae, in which 
the last two pairs of legs are generally reduced in size, and are 
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