NO. 19.] ECHINODERMS OF CONNECTICUT. 1 33 



Thyone briareus (Leseur) 



Common Thyone 



Plate XXIX, fig. 5 ; Plates XXX and XXXI. 



This species is distributed from Vineyard Sound to the Gulf 

 of Mexico, occurring from near low-water mark to a depth of 

 ten fathoms on both sandy and muddy bottoms. In certain local- 

 ities it is very abundant, while in seemingly equally favorable 

 situations it does not occur. It is commonly found buried in soft 

 mud in shallow water, often with its body bent into a U-shape, 

 with both extremities at the surface of the mud. In this position 

 its much branched, purplish tentacles stretch out on the surface 

 of the mud in search of the fine particles of organic matter which 

 constitute its food. The posterior end, with the cloacal aperture 

 usually widely opened, likewise reaches the surface of the mud 

 and alternately sucks in and discharges the water used in res- 

 piration. The species is often found at the bottom of streams 

 and creeks where the water is decidedly brackish. 



The color of the body is purplish, brownish, or blackish, the 

 pedicels lighter, often with a reddish cast, and the terminal disks 

 yellowish. 



The body when mature may become six or even nine inches 

 in length when fully extended, most individuals, however, being 

 about three or four inches long and an inch or more in diameter. 

 In shape, the animal is largest in its middle portions, being some- 

 what narrower anteriorly, and tapering decidedly toward the 

 posterior end (Plate XXXI) ; but the whole body may become 

 regularly oval or much rounded in certain states of contraction. 



The mouth, situated in the center of the anterior end, is sur- 

 rounded by a crown of ten tentacles, of which the two ventral 

 are much smaller than the others. All are profusely branched, 

 as shown in Fig. 21. The bases of these tentacles and their 

 larger branches are stiffened by the development of numerous 



Explanation of Plate XXXI. Thyone briareus. 



Fig. 1. Portion of one of the oral tentacles, showing the terminal finger- 

 like processes. Much enlarged. 



Fig. 2. Large specimen with oral tentacles expanded, and pedicels fully 

 extended. Natural size. 



Fig. 3. Preserved specimen with oral tentacles partially contracted. 

 Natural size. 



