INTRBUCTION 5 



PRINCIPAL PHYLA OF ANIMAL KINGDOM 1 



1. Protozoa. Single-celled animals; often colonial; sperm 

 and egg cells usually wanting. 4400 (2000). 



2. Porifera. Sponges. Triploblastic (?) ; radially symmetri- 

 cal, number of antimeres variable; body wall permeated by 

 innumerable pores and usually supported by a skeleton of spicules. 

 600 (800). 



3. Coelenterata. Jellyfishes, polyps, and corals. Diplo- 

 blastic; radially symmetrical, with four or six antimeres; single 

 gastro- vascular cavity; no anus; body wall contains peculiar 

 bodies known as nematocysts or stinging cells. 3000 (1780). 



4. Ctenophora. Sea walnuts or comb jellies. Triploblastic; 

 radial combined with bilateral symmetry; eight radially arranged 

 rows of paddle plates; anus present. 1000 (no fossils). 



5. Platyhelminthes. Flat worms. Triploblastic; bilaterally 

 symmetrical; single gastro- vascular cavity; no anus; presence 

 of coelom doubtful. 1600 (no fossils). 



6. Nemathelminthes. Round worms. Triploblastic; bi- 

 laterally symmetrical ; possess a tubular digestive system with an 

 anus; ccelom present. 1000 (no fossils). 



7. Rotatoria. Wheel animalcules. Triploblastic; bilaterally 

 symmetrical; coelom present; a pair of ciliated disks on the an- 

 terior end. 350 (no fossils). 



8. Bryozoa. Moss animals. Triploblastic; bilateral sym- 



1 Zoologists do not agree as to the number of phyla into which the animal 

 kingdom should be divided. Some authorities recognize only eight, while 

 others maintain that there should be as many as twenty, or even more. Two 

 sub-kingdoms are generally recognized, Protozoa (Phylum i) and Melazoa 

 (Phyla 2-15). Recently many zoologists have come to believe that the 

 sponges (Phylum 2) should be separated from other metazoons and called 

 the Parazoa. The animals in Phyla 1-14 are usually called invertebrates to 

 distinguish them from the vertebrates (15). Phyla 14 and 15, with a few ani- 

 mals of somewhat doubtful relationships, are commonly placed together 

 under the group Chordata, and are known as chordates. Phyla 2-4 include 

 animals without coeloms and are known as Accelomata in contrast to phyla 

 5-15, which contain animals with a coelom and are termed Calomata. 



