26 



Animal Life by the Sea-shore. 



Gastropods are characterised by a marked asymmetrj^ the greater 

 part of the body being coiled up spirallj' in a shell, and the foot 

 expands into a broad flat sole, by the muscular movements 

 of which a creeping movement is effected. The head is distinct 



f .'.. « 



I'lG. 



23. WHELK AND ITS EGG-CAPSULES. 



and pro^'ided with eyes and one or more pairs of tactile tentacles 

 which, in some forms, our garden snail for instance, carry the 

 eyes. One of the largest and best known of the British marine 

 types is the Whelk [Buccimtnt uiidaiutn), which displa3's all the 

 characteristic features of the group (Fig. 23). When fully "extended 

 the animal is not unlike a land-snail in general shape ; the head, 

 however, bears but a single pair of tentacles, at the base of which 

 the small eyes are situated. Another conspicuous character 

 which distinguishes it from the land-snail is the operculum, 

 a circular calcified disc carried on the posterior dorsal side 

 of the foot, forming a kind of lid closing the opening of the shell 

 when the animal completely withdraws into it. The mantle 

 cavity containing the gill is on the left side of the body, within 

 the shell, and, in order to allow the access of water, the opening 

 of this chamber is produced into a long tubular siphon, a con- 

 trivance which is characteristic of the marine snails. The WTielk 

 holds a very secondary position as an article of food ; it is, 

 however, extensively fished for on the East Coast, where the 

 sum derived from this fishery has been estimated at over twenty- 

 five thousand pounds per annum. Clusters of the Whelk's 

 egg-capsules are very familiar seaside objects, being frequently 

 washed ashore ; the whole mass of spawn has a honejxombed 

 appearance and consists of a large number of parchment-like 

 cells, each of which contains many small eggs. The majority 

 of small snail-'^ke creatures, which we find In-ing in rock-pools 



