No. 19.] ECHINODERMS OF CONNECTICUT. 15 



likewise discoid, and covered with minute brownish spines; but 

 is easily recognized by having five large openings, called lunules, 

 which pass quite through the body from one surface to the other. 

 Class 4. Holothuroidea: Holothurians, or Sea-cucumbers. — 

 The members of this group differ widely in general appearance 

 from those of the other classes. Our native species all live be- 

 neath stones or burrow in the sand or mud. Their bodies are 

 cylindrical and elongated, presenting a closer superficial resem- 

 blance to worms than to any of the other groups of Echinoderms. 

 This worm-like appearance is greatly enhanced by the absence 

 of any closely connected skeletal structures, and by the soft, bag- 

 like, highly muscular skin. The skin has, however, isolated cal- 

 careous plates, often of such peculiar and definite shapes that the 

 species are easily recognized by even a single plate. The mouth 

 is situated at one end of the body, and is surrounded by a circle 

 of branched tentacles. The anus is at the opposite end of the 

 body. The animals move both by means of sucker-feet and by 

 worm-like contractions of the body. 



In Long Island Sound there are probably six species belong- 

 ing to this class, although only four of these have as yet been 

 recorded from Connecticut waters. The common Thyone 

 (Thy one briareus) lies buried in soft mud in shallow water in 

 great numbers in certain localities. Sometimes the animals have 

 only the posterior end of the body projecting above the surface 

 of the mud, but at pther times they show also the anterior end 

 with its circle of branched tentacles of black or purple color. 

 The two other species of Thyone, T. unisemita and T. scabra are 

 rare, and occur only in rather deep water. 



Our fauna includes also two species with very slender bodies 

 belonging to the genus Synapta. These are peculiar in having 

 calcareous plates in the form of perfectly shaped anchors im- 

 bedded with other plates in the skin. Synapta inhcsrens is white 

 in color, while Synapta roseola is pink or reddish. Both live in 

 sandy localities between tides. 



Finally, there is the beautiful sea-cucumber (Cucumaria 

 pulcherrima) , which is rarely seen alive, but specimens of which 

 are sometimes thrown up on the beach by the waves following 



