212 MARINE INVERTEBRATES 



FAMILY HELIASTERIDJE 



GENUS Heliaster 



H. multiradiata. Spines on the upper surface of rays in five rows, 

 but close to the disk proper become reduced to one row. Found on 

 the coasts of Lower California and Mexico. (Plate LIV.) 



The Asteriidce have the following characteristics : four rows 

 of tube-feet; ossicles small and unequal; spines isolated or 

 grouped ; pedicellariaB of two forms, forceps-like and scissors-like 

 respectively. They include the very common forms found on all 



beaches. 



GENUS Asterias 



A. vulgaris. The common starfish of the Atlantic coast, from Long 

 Island Sound to Labrador. It occurs at low-water mark and extends into 

 deep water. It has five arms, which taper to a point. Large specimens 

 measure fifteen inches across. The upper surface is rough, being cov- 

 ered with short spines, which are largest and thickest at the edges of the 

 rays, and surrounding them are the pedicellaria3. The color varies from 

 pink, yellow, and brown to purple. 



A. Forbesii. The common starfish of the Atlantic coast, from Massa- 

 chusetts Bay to the Gulf of Mexico. This species resembles very closely 

 A. vulgaris, but can be distinguished from it by the madreporic plate, 

 which is bright orange, while in the former it has the same color as the 

 animal ; also the arms are a little swollen at the base and terminate more 

 bluntly. These two species are very destructive to oyster-beds, espe- 

 cially where their ranges overlap. It is computed that they destroy 

 annually two hundred thousand dollars' worth of oysters. Vast numbers 

 congregate where the feeding-ground is good, and move in long lines from 

 place to place. The oystermen dredge over the beds and bring them 

 up in thousands, then steam them or throw them on the shore above 

 high- water mark. (Plate LIV.) 



A. ochracea. The common starfish of the Pacific coast, from Sitka to 

 San Diego. Five rays, each hardly twice as long as the diameter of 

 the body ; spines running irregularly over the surface, but forming a 

 pentagon at the middle of the disk and inclosing the madreporic plate ; 

 diameter eight inches. It is very common near San Fx-ancisco on rocks 

 at low- water mark. (Plate LIV.) 



A. gigantea. Body very large and swollen; six rays, somewhat less 

 in length than twice the diameter of the disk ; aboral surface covered 

 with numerous short, blunt, equidistant spines of uniform size and 

 regularly distributed ; spines contracted at the base and striated ; diam- 

 eter two feet. Found on the California coast. 



