114 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



CLASS IV. HOLOTHUROIDEA 



The animals included in this class are sometimes called sea- 

 cucumbers. They are, however, not so well- known to people 

 other than naturalists as are the other classes, and most of them 

 can hardly be said to have any English names. 



The six species of holothurians found along the Connecticut 

 coast or in reasonable proximity thereto are all limited to certain 

 restricted localities, and their presence in any particular spot 

 cannot be predicted with any considerable degree of certainty. 

 In general, a muddy bottom below low-water mark is favorable 

 for the large, brown or blackish Thyone briareus, while the others 

 prefer sandy localities, the two species of Synapta occurring fre- 

 quently between tides, and the Cucumaria only below the ordinary 

 tides. The two other species, Thyone unisemita and Thyone 

 scabra, have not yet been recorded from Connecticut waters, but 

 their presence in Narragansett Bay and near the eastern end of 

 Long Island Sound makes it probable that they actually occur 

 within the limits of the Sound, and that future investigations will 

 reveal their presence in these waters. 



STRUCTURE 



These animals have but little superficial resemblance to the 

 other classes of Echinoderms, although in their general anatomi- 

 cal structure they show their relationship. In contrast with the 



EXPLANATION OF PLATE XXIX. 



Fig. I. Synapta roseola. Five times natural size. The two longitudinal 

 lines represent two of the five bands of longitudinal muscles. 



Fig. 2. Tentacle of same species, with seven digits. Much enlarged. 



Fig. 3. Synapta inharens, with the twelve tentacles surrounding the widely 

 opened mouth. The body is strongly contracted and shows 

 the constrictions due to action of the circular muscles. Along 

 the axis of the body one of the bands of longitudinal muscles 

 is shown. Five times natural size. 



Fig. 4. Tentacle of same species, with nine digits. Much enlarged. 



Fig. 5. Thyone briareus. Two-thirds natural size. The dorsal surface 

 is toward the top of the page, the lower, rounded margin 

 being in the mid-ventral line. 



