MOLLUSCA 393 



ECHINODERMATA 



This sub-kingdom of the Invertebrates comprises animals of 

 peculiar interest, and often of wonderful beauty. They are also 

 highly characterized by their almost universal assumption of the 

 "star" form, which we shall at once recognize in such names as 

 Stone-Lilies, Star-Fishes, Sea-Urchins, &c. From this radiate 

 character this great group used to be known, in association with 

 jelly-fishes and sea-anemones, as the Radiata. But the creatures 

 we have named, and their immediate relations, show something 

 of an intestinal cavity and system, which the jelly-fishes and sea- 

 anemones do not have; and further, they are related to higher 

 creatures by the possession of a vascular system (i.e. of blood- 

 vessels). They are, therefore, separated from their old friends of the 

 "Radiate" group, and are now known as the ECHINODERMATA 

 {le. "the hedgehog-skinned"); while the jelly-fishes, corals, sea- 

 anemones, and their allies are grouped into another sub-kingdom 

 and are termed the Ccelenterata. 



MOLLUSCA 



The Mollusca form a sub-kingdom in the animal world of no 

 mean proportions. More than 50,000 living species are known, 

 and the rocks are full of the fossil forms of species that once lived. 

 As a rule they are small creatures, such as the mussel, oyster, peri- 

 winkle. But some, of a different style from these, such as cuttle- 

 fishes, reach to an enormous size. 



They belong to the Invertebrates and are soft-bodied, as their 

 name implies (Lat. mollis, soft). But they use lime in their life 

 economy just as much as the Vertebrates do, only in a different 

 way. Most of them build up limy external coverings, either in one 

 piece, as in the garden snail or periwinkle; or in two pieces, as in 

 the oyster and pecten ; or in more than two pieces, as in the pholas 

 and chitons. 



