GASTROPODA. 



29 



water, but a few species live upon floating seaweed in the open 

 sea. Over a hundred species exist on the British coast, the 

 majority of which are, however, very small. They are chiefly 

 carnivorous, feeding on other mollusks, sea-anemones, &c. 



NlTCLEOBRANCHIATA. 



The Heteropods or Nucleobranchs include the Atlantidce, Carin- [Case 

 aria, &c, and may be considered aberrant Gastropods organized for 12f'J 

 swimming in the open sea. The Atlantas are found in great 

 numbers in warm latitudes, and are provided with a glassy, thin, 

 flat, spiral shell, not unlike a keeled ammonite. The glassy shell 

 of the Carinaria is one of the most beautiful structures of any 



Fig. 18. 



Glassy Nautilus (Carinaria lamarckii). 

 a, proboscis ; b, tentacles ; c, shell ; d, gills ; e, foot ; f, sucker. 



mollusk, and at one time was such a rarity that £100 are said 

 to have been given for a single specimen, which at the present 

 time is perhaps worth only a few shillings. Species of Carinaria 

 are found in the Mediterranean and warmer parts of the Atlantic 

 and Indian Oceans. The animal is large, semitransparent, and 

 elongate, with a compressed fin-like foot which projects from 

 the body, and is used in swimming. The gills are placed towards 

 the hinder part of the back and covered by the shell. They 

 feed on jelly-fish of various kinds, and probably on other soft 

 animals. 



