ZOOGENESIS 



numerous teeth set in a radula, or a beak; various special 

 sense organs present; very rarely elongated and w^orm-like 



MOLLUSCA 



k^ body divided into numerous segments and usually much elon- 

 gated; ventral nerve cord almost invariably with a swelling 

 or ganglion in each segment; almost invariably with chitin- 

 ous setas or bristles embedded in and secreted by pits in the 

 skin 



Annelida 

 i"^ body enclosed within a pair of shells, one of 

 which is dorsal and the other ventral 



Brachiopoda 

 h"^ body completely enclosed in a usually tough or 

 hard segmented external skeleton; with 

 jointed legs, and usually other jointed 

 appendages, in the young or adult, or in all 

 stages; jaws formed of modified legs 



Arthropoda 

 g^ a complicated water-vascular system, derived 

 from the coelom, present; body in the adult 

 more or less perfectly radial, usually in five 

 divisions, but bilateral in the younger stages; 

 body wall with abundant calcareous deposits 

 usually forming plates which generally bear 

 spines 



ECHINODERMATA 



p no body cavity; a protrusible proboscis lying in a 

 sheath running the whole length of the animal 

 on the dorsal side of the intestinal canal 



Nemertea 

 e^ without a vascular system 

 f- mouth armed with chitinous teeth or stout bristles; 

 size moderate; no asexual reproduction of any 

 kind 

 g^ body fish-like, with fins, divided internally into 

 three segments; coelom highly developed, with 

 three pairs of chambers separated by transverse 

 septa; both sexes in the same individual; 

 pelagic 



Ch^tognatha 



