The Animal Kingdom 347 



Branch C. Eumetazoa. Animals of tissue or organ grade of construc- 

 tion. 



Grade 1. Radiata. Animals with primarily radial symmetry. Mesoderm 

 primarily of ectodermal origin ; digestive cavity the only cavity of 

 the body, without organs. 



Phylum Coelenterata or Cnidaria. Mostly with radial sym- 

 metry and with stinging cells, the nematocysts. Examples : 

 hydra, jellyfish, corals. 

 Phylum Ctenophora. Animals with biradial symmetry, with- 

 out stinging cells. Example: comb jellies. 



Grade 2. Bilateria. Animals with bilateral symmetry or secondarily 

 acquired radial symmetry, of organ grade of construction, meso- 

 derm derived from entoderm. 



Acoelomate animals. 



Phylum Platyhelminthes. Flattened worms without anus. Ex- 

 amples : planaria, flukes, tapeworms. 



Phylum Nemertina. Usually elongated worms, with anus and ever- 

 sible proboscis. Example : nemertean worms. 



Pseudocoeloniate animals. 



Phylum Nemathelminthes. Aquatic, terrestrial, or parasitic worms 

 possessing cylindrical bodies; often with bristles but devoid 

 of cilia. Example : roundworms or nematodes. 



Phylum Rotifera. Anterior end of body bearing a ciliated wheel-like 

 organ, the corona. Pharynx with internal jaws. Example : the 

 rotifers or wheel animalcules. 



Phylum Gastrotricha. Pharynx without jaws, cilia present in some 

 areas, with adhesive tubes. Example : gastrotrichs. 



Phylum Kinorhyncha. Without cilia, but provided with spines, an- 

 terior end can be withdrawn ; superficially the body appears seg- 

 mented. Example : kinorhynchids. 



Phylum Nematomorpha. Cylindrical animals, ends of digestive 

 tract degenerate in adults, free-living adult, and parasitic larva. 

 Example : hair worms. 



Phylum Acanthocephala. Parasitic animals without a digestive 

 tract, with an anterior proboscis bearing hooks. Example : 

 thorny-headed worms. 



Phylum Entoprocta. Animals with looped intestine which opens 

 near the mouth ; anus and mouth surrounded by ciliated ten- 

 tacles. Example : moss animals. 



Phylum Priapulida. Warty animals with a superficially segmented 

 trunk. Example : priapulids. 



