20 GENERAL ZOOLOGY 



10 (9) Skin usually spiny; body a tube within a tube; marine. Star- 



fishes, sea-urchins, brittle stars, sea-cucumbers, stone-lilies: 



Phylum IX, ECHINODERMATA. 



11 (4) Bilaterally symmetrical. Have anterior (front), posterior 



(hind), right and left, dorsal (back), and ventral (belly) 

 regions 12 



12 (15) Body soft, flat, worm-like 13 



13 (14) One opening into digestive cavity; or no digestive cavity. 



Phylum V, PLATYHELMIA. 



14 (13) With mouth and anus Phylum VI, NEMERTINA. 



15 (12) Body not flat and leaf-like 16 



16 (17) Body cylindrical, worm-like; without anterior ciliated* lobes. 



Phylum VII, NEMATOIDEA. 



17 (16) Body not as described under 16 18 



18 (21) Small, often microscopic, aquatic animals; solitary or growing 



in branching plant-like colonies 19 



19 (20) Microscopic worm-like animals with two ciliated* lobes at the 



anterior end and a chewing stomach within the body. 



Phylum VIII, ROTIFERA. 



20 (19) Attached colonial animals which have a superficial radial 



symmetry Phylum X, BRYOZOA. 



21 (18) Larger animals; often possessing a hard shell which may cover 



the body 22 



22 (23) Stalked attached marine animals with a shell composed of two 



(dorsal and ventral) valves. Lamp shells. 



Phylum IX, BRACHIOPODA. 



23 (22) Soft-bodied animals, usually with a shell and a ventral muscular 



"foot" Phylum XIV, MOLLUSCA. 



24 (3) Body metameric and bilaterally symmetrical 25 



25 (28) No jointed appendages, body worm-like (snakes belong 



under 30) 26 



26 (27) Microscopic animals, with ciliated lobes at the anterior end of 



the body and a chewing stomach within. 



Phylum VIII, ROTIFERA. 



27 (26) No ciliated lobes at anterior end; body with minute bristles 



along the sides or with an adhesive sucker at one or both ends. 



Phylum XII, ANNELIDA. 



28 (25) Jointed appendages (except in limbless amphibians, snakes, 



and limbless lizards) 29 



29 (30) External skeleton (turtles, which have both exo- and endo- 



skeletons, belong under 30) ; no chorda. 



Phylum XIII, ARTHROPODA. 



30 (29) Endoskeleton; chorda or backbone present. 



Phylum XV, CHORDATA. 

 * Cilia are microscopic hair-like processes which usually wave actively. 



