14 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [BuU. 



the slender-armed starfish {Asterias tenera) and the blood 

 starfish (Henricia sanguinolenta) . 



Class 2. Ophiuroidea: Ophiurans, Serpent Stars, or Brittle 

 Stars. — In these forms the body consists of a flattened, circular 

 central disk, from the under side of which the usually slender, 

 round arms, with a large number of movable joints, extend 

 radially. These arms are sharply marked off from the disk 

 (Plate I), and are provided with strong muscles, which enable 

 them to be moved in nearly all directions and to be bent in sinuoiw 

 or serpentine lines. By the movements of these arms the body 

 is carried rapidly from place to place, and the flexibility of the 

 arms enable the animal to hide away in a very narrow crevice. 

 The mouth is situated as in the starfish, but there is no intestinal 

 opening. 



The ophiurans are represented in Long Island Sound by five 

 species, only two of which occur abundantly. They comprise the 

 following: the green serpent star (Ophiura brevispina) , the daisy 

 serpent star (Ophiopholis aculeata), the small gray serpent star 

 (Amphipholis squamatd), and the less common species, known 

 as Amphioplus abditus, and Amphioplus macilentus. 



Class 3. Echinoidea: Echinoids, or Sea-urchins. — Body 

 nearly circular in outline, hemispherical, or flattened and discoid; 

 without projecting arms. The calcareous plates inithe skin form 

 a compact encasement for the body except in the mouth region. 

 The case is called the shell or, more properly, the test The 

 mouth is usually in the middle of the oral surface. The ambulacra! 

 areas, with numerous sucker-feet, in the more typical forms, 

 extend around the body as meridians from the mouth nearly to 

 the opposite pole. The spines are movably articulated with the 

 plates on which they rest. 



In Long Island Sound there are four species of echinoids 

 which differ so widely in general appearance as to be easily dis- 

 tinguished. The common purple sea-urchin (Arbacia punctulata) 

 has a hemispherical test, with long, dark, reddish or purple spines. 

 The green sea-urchin (Strongylocentrotus drSbachiensis) has 

 shorter spines of a greenish color. The common sand-dollar 

 (Echinarachnius parma) is very flat and covered with min 

 brownish spines. The key-hole urchin {Mellita pentapora)^ is 



