INVERTEBRATE ZOOLOGY. 23 



Supplementary Class. Planuloidea. . . .Minute endoparasites without mouth 



or intestinal him en. resembling the pla- 

 nula larva of Cnidarian polyps. There 

 are two groups : the Dicyemidae. found 

 in the nephridia of Cephalopods, and the 

 Orthonectidae, in Ophiuridea, Turhellaria 

 and Nemertea. They have been^consid- 

 ered as Mesozoa, between Protozoa and 

 Metazoa. but are more probably Cnidaria, 

 reduced by parasitism. 



Type III. Ctenophora. 



Class I. Tentaculata With two long, prehensile, thread-like 



tentacles. -^ Pleurohrachia. 

 Class II. NuDA Tentacles wanting. -^ Beroe. 



Division II. HETERAXONIA. 

 Type IV. Zygoneura. 



Sub-type I. Protonephridozoa {Scolecida). 

 Cladus I. Platodes. 



Class I. TuRBELLARiA Small, free-swimming Platodes, of oval 



shape ; bodj' very contractile and covered 

 with cilia. 



Order 1. Rhal)docoela Intestine a straight, unbranched tube. 



Pharynx simple : small fornis. 

 ■^ Jile.sostomiiin. 



Order 3. Dendrocoela Intestine dendritic. Pharynx tubular. 



Larger forms, very flat. 



Sub-order 1. Trichula Intestine with three main trunks — one 



anterior, and two posterior. -^Planaria. 



Sub-order 2. Pohjclada Intestine like foregoing, but with more 



than two posterior branches. 

 ■^ Planocera. 



Class II. Trematodes Parasitic Platodes. Body of adult not 



ciliated, but generally furnished with 

 sucking-discs. Intestine much as in 

 Triclada. 



