ARTHROPODS. CLASS CRUSTACEA 103 
which they poke into the face of any intruder. While 
the anemones or hydroids are made to do valiant service 
Fic. 60.—Hermit-crab (Pagurus bernhardus) in snail shell covered with Hydractinia. 
with their nettle-cells, they also enjoy the advantages of 
a large food-supply which is attendant upon the free ride. 
104. The crabs—The most highly developed Crustacea 
are the crabs or short-tailed decapods which abound between 
tide-marks alongshore, and in diminishing numbers extend 
to great depths. The cephalothorax is usually relatively 
wide, often wider than long, and the greatly reduced abdo- 
men is folded against the under side of the thorax. Corre- 
lated with the small size of the abdomen, the appendages 
of that region disappear more or less, but the remaining 
appendages are similar to those of the crayfish or lobsters. 
All these different parts, however, are variously modified in 
each species to fit it for its own peculiar mode of life. In 
some forms, such as the common cancer-crab (Fig. 61), the 
legs are comparatively thick-set and possessed of great 
strength, enabling them to defend themselves against most 
enemies. On the other hand, there are the spider-crabs 
with small bodies and relatively long legs, withal weak, and 
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