MOLLUSCS 95 



the bottom and form a layer of ooze many feet in depth. 

 These tiny creatures, with fleshy wing-like expanses of the 

 feet and transparent glassy shells, constitute a vital food 

 supply of many whales. 



The Nudibranchs or Naked Keeled Molluscs, abundant 

 in all seas and at all depths, have parted with every trace 

 of shell, though a distinctly formed spiral shell is nearly 

 always possessed by embryos whilst yet within the egg 

 capsule. The Nudibranchs have much the general appear- 

 ance of shell-less snails, but the gills and extensions of 

 other organs stand erect and naked in rows upon the 

 creature's back. These often assume most extravagant 

 forms and vivid colours, frequently mimicking the sea 

 anemones, corals, sponges, etc. y upon which the creatures 

 feed. A remarkable feature of this diet is that the stinging 

 cells of the sea anemones and the hard spicules of the 

 sponges actually find their way high up into the erect 

 clublike structures of the Nudibranch's back without 

 apparently giving any discomfort. The eggs usually 

 take the form of delicate ribbon-like structures, sometimes 

 arranged on shells, etc., in a neat spiral formation. The 

 larvas emerge as minute snails, which row themselves 

 through the water by means of two flaps fringed with 

 lashing cilia. 



Over a hundred kinds of Sea Slugs are recorded from 

 our shores, the largest, Triton {Trttonia hombergi), reaching 

 about nine inches in length. A few species are pelagic, 

 swimming at the sea surface and eating larval fish, jellyfish 

 etc., whilst some deep-sea forms are illuminated with 

 hundreds of light organs. 



