244 ANIMALS OF THE SEA FLOOR 



(Entomostraca). It is perhaps not out of place to 

 suggest here that, in order to capture these smaller 

 forms, the water in which dredged material has been 

 put to stand should be strained off through a piece 

 of fine silk. Of these Entomostraca, but very unlike 

 the rest in appearance, are the Cirripedes, including 

 both the stalked barnacles and the sessile acorn- 

 shells. The stalked forms are for the most part 

 found growing on floating objects, but there is one 

 genus (Scalpellum) with a short stalk, which is often 

 found in deep water attached to Hydroids or other 

 fixed objects (Fig. 159, p. 218). The sessile or acorn- 

 barnacles are most abundant between tide-marks or 

 in shallow water, but there are a few deep-sea species 

 which reach a very large size. Of the other Ento- 

 mostraca, the Branchiopods belong to the Plankton 

 (Chapter V.), but the Copepods and Ostracods have 

 many bottom representatives. 



There are two very large groups of Crustacea, num- 

 bering some thousands of species, which we may con- 

 veniently illustrate by the sandhopper and the wood- 

 louse. These are the Amphipods (Fig. 180) and the 

 Isopods (Fig. 179). They may be found everywhere, 

 and may, for the most part, be recognized by their 

 resemblance to the types above mentioned. One 

 section of the Amphipods, however, the ghost shrimps, 

 or Caprellids, differs very markedly from the rest. 

 The Caprellids may be recognized by their slender 

 skeleton-like bodies, their thin legs, the two front pairs 

 of which are armed with strong claws, and their 

 " looper "-like movements (Fig. 191, p. 265). 



The Cumacea, another group of small Crustacea, 

 living for the most part buried in mud, may be known 

 by their small nut-shaped bodies and their long slender 

 tails ending in a fork. 



