STOMATOPODA . 
2 73 
mediate between the typical members of the last and present series, the thorax being 
larger and broader than the abdomen, while the carapace covers all but the last 
five segments. The front angles of the carapace are produced to meet in a kind 
of beak in front of the head, and the eyes are generally united in a single cluster 
of ocelli. None of the thoracic limbs are prehensile or chelate. The first five 
segments of the abdomen have no appendages in the female, although such limbs 
are present in the male. In the sixth segment appendages are present in both 
sexes, and form a fork-like termination to the body. Two of the best known 
genera of the group are Cuma and Diastylis. The order, however, is relatively 
a small one, containing only a little over a hundred species. It has, nevertheless, 
a wide distribution, forms being met with in shallow and deep water in all seas, 
although the Arctic Ocean produces individuals of the largest size and in the 
greatest abundance. 
Order Isopoda. 
Unlike the last, this second order of the series exhibits great diversity of 
structure. As a rule, the posterior seven segments of the thorax are free, and 
at least the first three, and generally the first five segments of the abdomen are 
short and sometimes fused together, while the sixth is the largest, and bears the 
telson and a pair of appendages. The other abdominal appendages usually 
overlap, and are modified to act as gills. The seven thoracic limbs are generally 
large, and perform the function of walking or swimming organs, while the 
posterior five pairs at least have no exopodites. There are four pairs of jaws, 
namely, the mandibles, two pairs of maxillae, and one pair of maxillipedes. 
Although there are many exceptions, it may be said that, as a rule, the body is 
broad, short, and flattened. Corresponding to the structural variations, the 
Isopods exhibit great diversity of habits and habitat. Most are marine, occurring 
in shallow waters or at great depths. Some live in fresh water, others on land, 
while others have taken to a parasitic life, and have thus to a great extent lost the 
characters of the order. 
Of the five tribes, the Valvifera have the posterior pair of abdominal 
appendages, or uropods, transformed into valves or flaps, covering part of the 
lower surface, and constituting a chamber for the gills. The tribe contains two 
families, the Arcturiclce and Icloteidce. The former are distinguished by their 
slender cylindrical shape, long lower antennae, and the length of the fourth 
thcf acic segment, which separates the posterior three pairs of thoracic legs from 
the anterior pairs by a wide space. The anterior thoracic feet are slender and 
hairy on the inner side, while the posterior feet are strong and prehensile, and 
enable the animal to fix itself to the branches of corallines. I11 the Idoteidce the 
body is longish and narrow, the thoracic segments being all of about the same 
size and shape, and their appendages short, stout, and used for walking. The 
anterior segments of the abdomen are short, and the posterior fused into a 
caudal shield. The species of the genus Idotea live in shallow water, and 
frequent places where there is an abundance of decomposing seaweed. They are 
essentially carnivorous, feeding on dead fish, worms, and molluscs. 
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