THE SEA BOTTOM 



63 



found here, also the common brittlestar, Ophiocoma 

 (Plate 24), and many starfish such as Asterias rubens, and 

 A. glacialis, a related larger, grey species, though these 

 latter wander far in the pursuit of food. In cracks and 

 holes live the sea gherkins, their whitish bodies hidden, and 

 only the tentacles exposed. There is the usual abundance 

 of crustaceans, such as the lobster (Plate 113), and many 

 crabs, including the edible species and several spider crabs 

 (e.g. Inachus, Hyas, Macropodia) which have delicate 

 limbs and disguise themselves with pieces of weed fastened 

 to small hooks on the 

 shell, and so survive in 

 spite of their weakness. 

 Prawns of various kinds 

 are always to be found 

 among rocks. 



Burrowing animals are 

 the characteristic mem- 

 bers of the sandy-bottom 

 fauna. The burrowing 

 bivalves are too numer- 

 ous to mention. The 

 common cockle is never 

 found, but the spiny 

 cockle — a larger species 

 with its shell covered 

 with powerful spines, the better to enable it to grip the 

 sandy gravel — takes its place. Associated with the bivalves 

 are carnivorous snails which bore into and feed upon them. 

 Burrowing sea urchins, such as Echinocardium (Plate 20) 

 and Spatangus, and the little heart-urchin, Echinocyamus, 

 live in sand, and also one starfish in particular, named 

 Astropecten (Fig. 9), which has pointed instead of sucker- 

 like tube-feet. It burrows in sand, capturing and swallow- 



Fig. 9. — Astropecten. 

 A Starfish which burrows in sand (x J). 



