ROLL CALL 37 



PHYLUM VI — NEMATHELMINTHES — Roundworms. 



Characteristics: Bilaterally symmetrical ; cylindrical, unsegmented, long 

 and slender worms ; usually a distinct alimentary canal with mouth and 

 anus ; primitive body cavity present ; papillae or spines at anterior tip of 

 body. 



Class I — Nematoda — Threadworms (TrichineUa, Trichuris, Necator, Oxyuris). 

 Characteristics : Members of this group art; l)oth free-living and parasitic 

 on plants and animals; mouth usually terminal and alimentary canal 

 composes a relatively straight tube with anal opening near posterior end 

 of body ; body cavity not lined by epithelium but bounded directly by 

 muscles of the body ; four thickenings of the ectoderm, one dorsal, one 

 ventral, and two lateral, produce ridges containing excretory canals and 

 nervous system ; sexes separate. 



Class II — Gordiacea — Hairworms {Gordius, Paragordius). 



Characteristics : Long, slender, and hairlike ; free-living adults in water ; 

 larvae usually parasitize aquatic insect larvae (often Mayflies) ; asually 

 reach a second host, as beetle or grasshopper, in which development con- 

 tinues ; escape to water made by breaking through body wall ; no lateral 

 lines present; body cavity hned by distinct peritoneal epithelium derived 

 from mesoderm ; eggs discharged into body cavity instead of to outside. 



Class III — Acanthocephala — Spiny-headed worms (Leptorhynchoides, Neo- 

 echinorhynchus, Macracanthorhynchus) . 

 Characteristics: Protrusible proboscis armed with hooks; alimentary 

 canal absent; reproductive sy.stem complex; entirely parasitic, larval 

 stage in Arthropods. 



h. w. h. — 7 



