Key to the Echinoderms of Friday Harbor, Washington'' 



Mildred Bush, 

 Universiti/ of Washington, Seattle. 



The area included in this paper is roughly San Juan County, Wash- 

 ington. All the material was secured b^^ means of a trawl and by shore 

 collecting at low tide. The aim is to make it easier to determine the species 

 of echinoderms in the vicinity of the Puget Sound Biological Station. 



The starfish range in size from the small 6-rayed Leptasterias. which 

 are from ^Z. to 3 inches in diameter, to the large Evasterias and Pycnopodia, 

 which are sometimes 2 feet or more in diameter. They vary in number of 

 rays from 5 or 6 to 20 or more (plate 7). 



Hybrids are common among the starfishes. Specimens may show the 

 general characteristics of Pisaster confertus but have some large capitate 

 spines like those of Pisaster ochraceus. The larger spines may be some- 

 what clustered, with a large capitate one in the center, as in Evasterias 

 suhnodosa. The species of Leptasterias are particularly hard to classify 

 because many young of larger 5-rayed species have 6 rays and a similar 

 arrangement of spines. They are specially hard to distinguish from 

 some Asterias types because the dorsal spines are similar, and each may 

 have 1 or no peractinal row of spines. There are evidences of crossing 

 among Evasterias species, especially of E. troschelii rudis and E. troschelii 

 suhnodosa. In these the size and form may be like the former while the 

 dorsal spines may have the nodular arrangement of the latter. Some 

 specimens show the feebly developed dorsal skeleton and few scattered 

 spines of Orthasterias, and the many rows of interactinal spines of Evas- 

 terias. The dominant type may be determined by the presence or absence 

 of the peculiar Orthasterias pedicellariae which in profile look like blunt 

 hooks (Fig. 30). 



In the classification of starfish, the form, number of rays, form and 

 arrangement of spines, and the form of pedicellariae are the most evident 

 dependable characteristics. The form and arrangement of the spines vary 

 in the different species, and these will be described in each. Figure 34 

 illustrates in general the position of the groups of spines mentioned in the 



♦EDITOR'S NOTE — Taxonomic articles bringing together the species of 

 larger groups so far as tliose species are found in the vicinity of ttie Puget 

 Sound Biological Station are encouraged on account of tlieir helpfulness in 

 researcli in almost every other field of zoology. With descriptions scattered 

 thruout nvimerous jf)urnals an ecologist, for example, might find it necessary to 

 spend most of liis first summer' locating ta.xonomically the animals with which 

 he wishes to experiment. 



(17) 



