CLASSIFICATION OF LIVING THINGS 143 



minal mouth and anus, coelom present, appendages 

 wanting. Body covered with a heavy cuticle. 

 Free living or parasitic. Pork worm (Trichinella), 

 vinegar eel, thread worms, 



PHYLUM ANNELIDA. Segmented worms, usually with a 

 well marked coelom. Internal organs segmentally 

 arranged. As a rule chitinous setae are embedded 

 in the skin. 



Class 1. Chaetopoda. Annelida with conspicuous setae. 

 The well marked coelom divided by septa. Earth- 

 worm, Nereis. 



Class 2. Hirudinea. Elongated, flattened annelida with 

 anterior and posterior suckers, without seise and 

 with median genital openings. Coelom much 

 reduced. Leeches. 



Class 3. Gephyrsea. Unsegmented worm-like animals 

 with a spacious ccelom not divided by septa, an 

 anterior anus and a single pair of nephridia. Setae 

 absent. 



PHYLUM MOLLUSCA. Bilaterally symmetrical, unseg- 

 mented animals, with a ventral foot, a mantle fold, 

 and usually a univalve or bivalve shell. The 

 central nervous system consists of a circum-eso- 

 phageal ring. 



Class 1. Lamellibranchiata. Symmetrical mollusca with- 

 out head; with bilobed mantle, bivalve shell, and 

 usually with lamellate gills. Clams, mussels, 

 oysters. 



Class 2. Gastropoda. Asymmetrical mollusca with a 

 distinct head usually bearing tentacles, a muscular 

 creeping foot, a continuous mantle fold and usually 

 a coiled shell of one piece. Snails. 



