HOLOTHUKIOIDEA 



40^ 



Fig. 244. — Calcareous deposits 

 of Tkyone fusus. x 200. 

 (From DanmarFs Fauna.) 



It is usually found on shell bottom, and covers itself with 

 fragments of shells, being therefore easily overlooked in the con- 

 tents of the dredge. On account 

 of the delicacy of its skin, it 

 often ruptures through the con- 

 traction of the animal on capture, 

 the pharynx with the characteristic 

 calcareous ring thus hanging out. 

 Development unknown. 



In British seas this species 

 appears to occur all round the 

 coasts from Plymouth to the Shet- 

 lands, and down to Cullercoats 

 on the east coast. Also known 



from the Rockall Bank. It is elsewhere distributed from the 

 Trondhjem Fjord to Madeira and the Mediterranean, in depths 

 of ca. 10-615 m. 



2. Thy one raphanus Diiben and Koren. (Fig. 242, 2.) 

 (Syn. Thy one Poucheti Barrois.) 

 Body thick, ovoid, attenuating posteriorly into a long, thin, 

 tail-like prolongation, the animal thus resembUng to some degree 



a radish. Usually it is bent 

 hke a U. Tube-feet less 

 numerous on the dorsal side 

 and wholly absent in the 

 posterior part of the caudal 

 prolongation. Deposits (Fig. 

 245, 1) rather large, smooth, 

 or more or less tuberculate, 

 fenestrated plates, lying so 

 close as to be partly im- 

 bricating, like scales. Col- 

 our in life yellowish or 

 brownish, fading in alcohol. 

 Attains a size up to 6 cm. 

 length. 



It lives on sandy or 

 muddy bottom, buried in the 

 ground, with only the tail- 

 end protruding above the 

 not a plankton-feeder, as are 

 directly ingests the bottom 



Fig. 245.— Calcareous deposits of Thyone 

 raphanus (1) and Th. serrifera (2). 

 X 14o. (From Danmark's Fauna.) 



surface, 

 usually 



It thus seems that it is 

 the Dendrochirotes, but 



