THE STARFISH 



Certain starfishes have many arms instead of only five.' In 

 still other starfishes the raj's are partiallj' connected by a mem- 

 brane like the web of a 

 duck's foot, so that the 

 whole outline is nearlj' 

 pentagonal (Fig. 244). In 

 extreme cases the outline 

 becomes strictly pentag- 

 onal or even approxi- 

 mately circular in plan, 

 like a sea-urchin. The 

 last species shows a transi- 

 tion between starfish and 

 urchin. 



The Serpent-stars. — In 



the serpent-stars (Ophiu- Fig. 243. — Solaster, a multi-rayed starfish. 

 ■ 1 2\ J.U Reduced. From LeunLs. 



oridea'^j the organs are 



not prolonged from the disk 

 into the arms, consequently 

 the arms may be thrown off 

 without injury to the ani- 

 mal; hence the name 

 " brittle-star." The brittle- 

 stars fall into two groups, in 

 one of which, the serpent- 

 stars, the arms are un- 

 branched,^ while in the 



^ It is so in the case of Sohistcr 

 endeca of the northern Athmtic 

 (Fig. 243). 



2 ophis, serpent ; oura, tail. 



" Fig. 245. 



Fig. 244. — .'Vrehiaster, a webbed starfi_sh. 

 Slightly reduced. Photo, by W. H. C. P. 



