248 DISCOVERY REPORTS 



4. Thalassema antarcticum sp.nov. Plate VII, figs. 3, 4. 



Occurrence. Falkland Islands: St. 1909. 132 m. 



Palmer Archipelago, SchoUaert Channel: St. 182. 278-500 m. 



HoLOTYPE. The introvert seemed to be fully expanded and was much longer 

 than the body, which was short and cylindrical. The body measured 27 mm. and the 

 introvert 52 mm. In preservative the introvert was straw-coloured with a darkened 

 thickened edge all round, while the body was grey-brown. In life, however, the colour 

 was more vivid, as the colour note made at the time of capture indicates : ' found 

 embedded in the heart of a dark green clayish rock, only the ribbon-like introvert 

 protruding through a chink in the surface of the rock and waving gently to and fro. 

 Body pale yellow-white, translucent, the viscera showing through. The introvert pale 

 milk-white, translucent, edged with opaque porcelain-white.' 



The surface of the introvert was smooth and the thickened edge had indentations at 

 intervals. The tip was not divided but had an indentation similar to those along the 

 sides. 



The body was smooth in appearance, and only under magnification were the very 

 small papillae visible. These papillae were very small, elongated, white bodies and 

 were seen only in the middle of the body. The skin at the extremities of the body was 

 somewhat corrugated. 



The longitudinal muscles were continuous. There were two yellow ventral setae. 

 These were rectangular in shape in the end portion when seen in full and are only 

 slightly bent at the tip when seen in profile. 



There was only one pair of segmental organs and they had no spiral appendages. 

 They were thin white tubes and narrowed at the lower end into a still thinner tube 

 which bore the funnel at its lower end. 



Holotype taken at St. 1909. Deposited at the British Museum (Nat. Hist.). 



At St. 1909 an introvert similar to that possessed by the type was also taken, and a 

 similar colour note attached to it. 



At St. 182 a much larger animal was taken, which seemed to belong to this species. 

 The body measured 67 mm. The introvert measured only 33 mm., this comparative 

 shortness compared with those at St. 1909 being due to contraction. Such a diflFerence 

 due to the state of the animal when preserved has been illustrated by Shipley (1899, 

 pi. xxxiii, figs. 5, 6, p. 338) in the case of Thalassema neptuni. The introvert was similar 

 in. appearance to the others mentioned. The ventral setae had been lost. The two 

 segmental organs were long thickish tubes, almost three-quarters the length of the 

 body and filled with small ova. 



This species differs from others of its genus possessing continuous longitudinal 

 muscles and a single pair of segmental organs, in the lack of papillae on the body and 

 in the long ribbon-like introvert. 



