ANIMALS CLASSIFIED 



183 



A horny fiber sponge. Notice that it is a 

 colony. One fourth natural size. 



the sponges of commerce. 

 With but few exceptions 

 sponges live in salt water 

 and are never free swim- 

 ming. 



III. Ccelenterates. 

 The hydra and its salt- 

 water allies, the jellyfish, 

 hydroids, and corals, be- 

 long to a group of animals 

 known as the C&lenierata. 

 The word " ccelenterate ' 

 (axiom = body cavity, en- 

 teron = food tube) explains 



the structure of the group. They are animals in which the real 

 body cavity is lacking, the animal in its simplest form being little 

 more than a bag. Some examples are the hydra, shown on page 

 179, salt-water forms known as hydroids, colonial forms which have 



part of their life free swim- 

 ming as jellyfish ; sea anemones 

 and coral polyps, tiny colonial 

 hydra like forms which build 

 a living or secreted covering. 



IV. Worms. - The worm- 

 like animals are grouped into 

 jl'ttirorms, roundworms, and 

 segmented or jointed worms. 



(a) Flatworms are sometimes 

 parasitic, examples being the 

 tapeworm and liver fluke. 

 They are usually small, ribbon - 

 or leaf-like and flat and live in 

 water. 



(6) Roundworms, minute threadlike creatures, are not often 



seen by the city girl or boy. Vinegar eels, the horsehair worm, 



the pork worm or trichina and the dread hookworm are examples. 



(c) Segmented worms are long, jointed creatures composed of 



Sea anemones. One half natural size. The 

 right hand specimen is expanded and 

 shows the mouth surrounded by the 

 tentacles. The left hand specimen is 

 contracted. (From model at the Ameri- 

 can Museum of Natural History.) 



