PHYLUM CCELENTEKA 



Classes 



1. Hydrozoa 



2. Scyphozoa 



(Scyphomedusae) 



3. Anthozoa or Actinozoa 



4. Ctenophora (not fossil). 



. Orders 



1. Gymnoblastea. 



2. Calyptoblastea. 



3. Graptolitoidea. 



4. Hydrocorallina. 



5. Stromatoporoidea. 



6. Trachomedusae (not fossil). 



7. Narcomedusae (not fossil). 



8. Siphonophora (not fossil). 



1. Stauromedusaa (not fossil). 



2. Peromedus83 (not fossil). 



3. Cubomedusae (not fossil). 



4. Discomedusas. 



1. Zoantharia. 



2. Alcyonaria, 



The Coelentera include hydro-ids, jelly-fishes, sea-anemones, 

 corals, and allied forms. The individuals are radially 

 symmetrical, and have only one internal cavity, the 

 cceleiiteron, which opens to the exterior by the mouth. 

 The body-wall consists of an outer layer of cells, the ecto- 

 derm, and an inner layer, the endoderm ; between these is 

 a gelatinous layer — usually quite thin, but in the jelly- 

 fishes of considerable thickness. Stinging cells known as 

 nematocysts or thread-cells are generally present in the 

 ectoderm. The canal-system, so characteristic of the 

 sponges, is absent. 



