2 SYNOPTIC KEY 



9(3? 5) Body bilaterally S3mimetrical or spirally coiled in part; 

 never radially symmetrical; sometimes bent so that 

 the mouth and anus lie near each other. 10 



10(33) Body soft and wormlike or covered with a hard shell 

 or other hard outer covering; no internal skeleton of 

 bone or cartilage making a skull and spinal column; 

 no gill slits opening to the pharynx. 11 



11(12) Small, more or less transparent aquatic forms in fresh 

 water, usually bearing a girdle or crown of cilia at the 

 anterior end upon a more or less disklike, often lobed 

 region. An internal gizzard with movable jaws. 

 Posterior part of body frequently segmented and worm- 

 like. Cilia may be restricted to ventral surface, or 

 absent in marine forms. Phylum Trochelminthes, p. 15 



12(11) Without such cilia in adult condition. 13 



13(22) Body not divided into segments either by constrictions 

 on the surface, by segmental bristles or segmental 

 appendages. 14 



14(18, 17) Flattened wormlike animals. 15 



15(16) Worms with a long proboscis inclosed in a sheath which 

 lies on the dorsal side of the animal dorsal to the diges- 

 tive tract. The proboscis is capable of extrusion 

 through an opening at the anterior end which may or 

 may not coincide with the mouth. Marine forms may 

 be large, fresh-water ones are small. (Pratt, 205; 

 W. and W., 454.) Phylum Nemertini 



16(15) Without a proboscis of the kind described above. Anus 

 always absent. Body usually flattened dorsoventrally, 

 may be leaf or ribbon-like. Free-living forms with 

 naked body bearing cilia, at least on the ventral 

 surface; parasitic forms covered by a thin cuticle. 

 Marine or fresh water. Flat worms, trematodes; 

 simplest tapeworms. Phylum Platyhelminthes, p. 13 



