190 THE BIOLOGY OF THE SEA-SHORE 



habits of shore animals, selecting one or two of the most 

 characteristic and best studied examples from each of the 

 chief phyla. 



Some Methods o! Feeding of Shore Animals. — The 

 majority of sea anemones expand their tentacles to seize 

 and paralyse any swimming or creeping organisms that may 

 wander within their grasp, and are not sufficiently strong to 

 escape. Small Crustacea are undoubtedly one of their 

 chief sources of food, and it is probable that many are 

 deceived by the alga-like appearance of some anemones and 

 alight upon their tentacles only to be conveyed to the mouth. 

 The captured animal is passed on from the outer to the inner 

 tentacles and finally placed within the mouth, which gapes 

 ready to receive it. At times the outer tentacles of some 

 species may sweep the ground, or one or more may become 

 elongated. Many Gasteropods are so protected by shell or 

 by slime coat that they can push their way through the 

 clutching tentacles ; in other cases a prolonged struggle 

 may ensue before the prey is either finally ingested or 

 succeeds in breaking away. Anemones are themselves 

 attacked by sea-slugs {Aeolidiella papulosa and others), 

 which rasp pieces out of the body wall (Fleure and Walton, 

 1907). 



Among Echinoderms, starfish are well known to feed on 

 mussels, oysters, and other bivalves. Several different 

 explanations have been suggested of the manner in which 

 the prey is overpowered and induced to open, such as the 

 influence of a chemical secretion, waiting for the adductor 

 muscles of the bivalve to relax, and so on. There seems no 

 doubt, however, that the exercise of force by the tube-feet 

 is the real cause of the victim's undoing. In order to over- 

 power a bivalve the starfish needs to rise into a mound with 

 the arms pressing closely together and tips closely investing 

 the victim, which is manoeuvred into a vertical position 

 between them. The position adopted resembles very 

 closely that used when spawning, which is illustrated in 

 Plate XL Half the tube-feet are then attached to one 

 valve and half to the other, and a pull in opposite directions 



