132 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



II. Phylum Coelenterata 



1 (4, 7). Animals of the hydroid type; sessile. 2 



2 (3). Nearly always colonial; body of the hydroids on the end of slender 

 stalks; without an esophagus, and gastrovascular cavity, a simple sac, not divided 

 by septa. Class Hydrozoa 



3 (2). Solitary or colonial; cylindrical or columnar, not divided into body 

 and stalk; with an esophagus, and gastrovascular cavity divided into com- 

 partments by partitions. Class Anthozoa 



4 (i, 7). Animals of the medusa type, solitary, free-swimming. 5 



5 (6). With a velum and of simple structure. Class Hydrozoa 



6 (5). Without a velum, and more complex in structure, usually with 

 highly branching gastrovascular canals. Class Scyphozoa 



7 (i, 4). Complex floating colonies containing both hydroid and medusa 

 types of individuals. Class Hydrozoa; Order Siphonophora 



III. Phylum Platyhelminthes 



1 (4). With mouth and digestive tract; not especially elongated, nor 

 divided into segments. 2 



2 (3). Free-living, ciliated forms, without suckers. Class Turbellaria 



3 (2). Parasitic, not ciliated; with at least one sucker, often more, often 

 hooks in addition. Class Trematoda 



4 (i). Without mouth or digestive tract; nearly always very long and 

 tapelike, and divided into segments (not true segments) ; parasites. 



Class Cestoda 



IV. Phylum Annelida 



1 (4). Segmental bristles present; indefinite number of segments; no 

 suckers. Class Chaetopoda 2 



2 (3). Bristles numerous, generally on lateral outgrowths, the parapodia. 



Subclass Polychaeta 



3 (2). Bristles few, set directly into the body wall; no parapodia. 



Subclass Oligochaeta 



4 (i). Segmental bristles absent; limited number of segments; with an 

 anal and an oral sucker. Class Hirudinea 



V. Phylum Echinodermata 



1 (8). With a well-developed skeleton of calcareous ossicles or plates; 

 usually spiny; radial; no tentacles. 2 



2 (3). Mostly sessile, attached by a stalk springing from the aboral surface; 

 if free, moving on the aboral surface. Class Crinoidea 



