304 Animal Biology 



rather isolated, small, calcareous plates. Branched, contractile tentacles surround 

 the mouth. Five rows of radially arranged rows of tube feet extend the length 

 of the body. The external surface is free from spines, cilia, and pincerlike pedi- 

 cellaria. The madreporite is internal. The sea cucumbers move about freely in a 

 lateral position near the bottom of the sea. They possess remarkable powers of 

 autotomy and regeneration. When stimulated, the muscles of the body wall con- 

 tract and set up an enormous pressure in the fluid of the body cavity. As a result, 

 many of the internal organs are pushed out and surround an attacking enemy. 

 The lost organs are usually soon regenerated. 

 Example: Sea cucumber (Fig. 111). 



M 



Fig. 109. — Diagram of the skeleton or "test" (with spines removed) of purple 

 sea urchin (Arbacia punctulata) of the class Echinoidea. Outline of plates of the 

 aboral surface, showing the four plates of the periproct (center) surrounded by 

 the five ocular and five genital plates at the ends of the ambulacral, R, and 

 interambulacral, /, zones, respectively; one genital plate marked M is the 

 madreporite plate; the ocular plate is smaller than the genital plate and is lo- 

 cated in the angle between two of the latter; T, tubercles for attachment of 

 spines; P^ pores for the tube feet. (From Coe: Echinoderms of Connecticut, State 

 Geological and Natural History Survey of Connecticut, Bulletin 19.) 



Class 5 — Crinoidea (kri -noi' de a) (Or. krinos, lily; eidos, resemblance). — 

 The five arms generally are branched with many smaller pinnules which give a 

 lilylike appearance. The tentacles are like tube feet but without the pouchlike 

 ampullae. The aboral plate usually has a heavy jointed stalk for temporary or 

 permanent attachment. Certain species have small holdfasts; others are second- 

 arily free swimming. Fossil remains of crinoids are very common in limestone 

 strata. 



Examples: Stone lily, feather star (Fig. 112) and sea lily. 



Phylum 9. Annelida (a -nel' i da) (L. annellus, a little ring; eidos, resemblance). 



General Characteristics 



These worms are elongated with a linear series of internal and external ring- 

 like segments (metameres). They possess bilateral symmetry. Setae, or skin 



