l8 SYNOPTIC KEY 



Phylum ECHINODERMA 



I (6) Arms present. 2 



2(3) Arms with small branches, called pinnules; animals 

 either sessile and attached by a stalk from the aboral 

 surface or if free, moving about with the oral surface 

 directed upward. (Pratt, 619.) Class Crinoidea 



3(2) Arms without pinnules, not sessile or stalked, moving 

 about on oral surface. 4 



4(5) Arms not sharply marked off from the disk; oral 

 surface of arm marked with a deep longitudinal groove. 

 (Pratt, 623.) Class Asterioidea 



5(4) Arms sharply marked off from the body; oral surface 

 without a deep longitudinal groove. (Pratt, 635.) 



Class Ophiuroidea 



6(1) Arms absent. . 7 



7(8) Body hard, globular, or disklike, bearing numerous 

 spines; oral tentacles absent. (Pratt, 638.) 



Class Echinoidea 



8(7) Body soft, not calcareous but with tough leathery wall; 

 spines absent; oral tentacles present. (Pratt, 646.) 



Class Holothuroidea 



Phylum MOLLUSCA 



I (6) No distinct head present; shell never spirally coiled. 2 



2(5) Shell when present not bivalve. 3 



3(4) Body naked or covered on dorsal surface by shell of 

 eight plates; marine. (Pratt, 482.) 



Class Amphineura 



4(3) Shell tusklike, cylindrical; marine. (Pratt, 490.) 



Class Scaphopoda 



5(2) Shell bivalve. The mussels, clams, oysters, etc. 



Class Pelecypoda, p. 19 



