32 LIFE BY THE SEASHORE. 



and sea-squirts, are here absent ; gills when present are out- 

 growths of the skin. 



I. PROTOZOA Minute, usually microscopic forms, im- 

 portant as furnishing food for higher forms. 



II. SPONGES. May be recognised by their spongy, 

 porous bodies, furnished with one or more open- 

 ings, and containing a skeleton of lime, flint, or 

 horn. The crumb-of -bread sponge and the purse- 

 sponge are common both in the fresh and dried 

 state. 



III. CCELENTERA. Hollow-bodied animals, including sea- 



anemones, jelly-fish, sea-firs, " dead men's fingers," 

 and many others. The mouth surrounded by 

 tentacles bearing stinging-cells is a very character- 

 istic structure. 



IV. UNSEGMENTED WORMS. The ribbon-worms have lank 



unsegmented bodies, very uniform throughout 

 their length, and eject a thread or proboscis 

 when alarmed. The Turbellaria are flat and leaf- 

 like, and move with a peculiar gliding motion. 



V. ANNELIDS, or SEGMENTED WORMS. The body is 

 divided into rings, or segments, which bear 

 lateral tufts of bristles. Very many live in 

 tubes, and then the bristles may be inconspicuous. 



VI. ECHINODERMS. Prickly-sldnned animals, usually with 

 much lime in the skin; the body is more or less 

 star-like, and the delicate, transparent tube-feet 

 are very characteristic. Starfishes, brittle-stars, 

 and sea-urchins are the commonest kinds. 



VII. ARTHROPODS. These, the animals with jointed legs, 

 are represented by the hard -coated Crustacea 

 shrimps, prawns, lobsters, crabs, sand-hoppers, etc. 

 which are very varied in form, but are recognised 

 by the segmented body, the jointed legs, the hard 

 coat, the two pairs of feelers. 



VIII. MOLLUSCA. The Bivalves, such as mussels and 

 oysters and so on, are readily recognised by tho 



