52 



SEA-SHORE LIFE 



gm^is which is found from North Carolina to Labrador, bnt is com- 

 mon only north of Cape Cod. In this starfish the arms are more 

 pointed than in .4. forhesii, the skin is not so rigid, and the madre- 

 poric plate is of the same color as back of the animal, which may be 



Fig . 25 ; Left : HORSESHOE CEAB. Ri^ht: COMMON STARFISH. 

 Bel07i<: (JREEN SEA-URCHIN. 



purple, yellow, brown or beautiful shades of pink or red. It ranges 

 from low tide level to a depth of 1200 feet. Many naturalists con- 

 sider these two forms to be identical, but the writer found that in 

 Asterias forhesii from Long Island Sound, 78 individuals in 10,000 

 had more or less than five arms, whereas in A. vulgaris from Mas- 

 sachusetts Bay only 23 in 10,000 had more or less than five arms. 

 It seems, therefore, that the southern form is more than three times 

 as variable as the northern. 



There is a minute red eye-spot at the tip of each arm of the 

 starfish. Hundreds of sucker-like tube-feet arise from a deep 

 groove that extends down the mid ventral side of each arm, and 

 between two of the arms on the upper side of the disk one may see 

 a bright colored area called the madreporic plate. Its situation 

 marks the sieve-like entrance to the water tubes of the starfish. 



