DESCRIPTION OF SPECIES 



117 



Pyura setosa (Sluiter) (PI. IV, fig. 2) 



Halocynthia setosa Sluiter, 1905, p. 472. 



For synonymy and references see Kott (1954), p. 126. 



Occurrence. St. 175: S. Shetlands. 



External appearance (PL IV, fig. 2). The single specimen is ovoid, 3-5 cm. long and 2-6 cm. high, 

 and almost completely covered with a thick coat of long stiff bristles. These bristles, which reach 

 13 mm. in length, bear many short pointed spines. 



Tentacles. There are about twenty-one compound tentacles of various sizes and a few small almost 

 unbranched ones. 



Dorsal tubercle. The dorsal tubercle is C-shaped with the open interval facing forward and a 

 little to the right. 



Branchial sac. The anterior part of the dorsal lamina is a toothed membrane, and for most of its 

 length the lamina is represented by long pointed closely crowded languets united basally by a narrow 

 membrane. The longitudinal bars on the six branchial folds are arranged thus: dorsal line 3 (31) 3 (16) 



3 OS) 5 6 ) 5 (29) 2 (3°) 2 endostyle. 



Gonads. The left gonad is within the intestinal loop, and the right gonad is a long horizontal sac. 

 The sperm duct and oviduct are short and turned upwards towards the atrial siphon. 



Test spines 

 Tentacles 

 Dorsal tubercle 



Dorsal lamina 



Branchial folds 

 Occurrence 



P. setosa 



Up to 21 mm. long 



About 16 



Horse-shoe with inrolled 



horns; facing forward 

 Series of languets, anterior 



ones small, posterior large 

 6 each side 

 Western and eastern 



Antarctic 



Table 34 



P. stubenrauchi 



Up to 5 mm. 



About 30 



Horse-shoe ; facing forward 



A membrane toothed at 



posterior end 

 4 each side 

 Strait of Magellan 



P. echinops 



'Short' 



About 38 



Horse-shoe, inrolled horns, 



facing forward 

 A membrane toothed except 



at anterior end 

 4 each side 

 North coast Argentine 



Remarks. P. setosa is a very distinctive species, but two other species P. stubenrauchi (Michaelsen) 

 and P. echinops Arnback have been described with similar characters, and the important features of 

 the three are shown in Table 34. 



It appears from this comparison that P. stubenrauchi and P. echinops are the same species as sug- 

 gested by van Name (1945); the name P. stubenrauchi has priority. 



P. setosa is distinguished from P. stubenrauchi by several characters, but principally the subdivision 

 of the dorsal lamina into languets and the presence of six branchial folds on each side. The two 

 species are nevertheless obviously closely related, having been derived from a common ancestor by 

 geographical speciation. 



Distribution. Antarctic (Graham Land, South Orkney Islands, Kaiser Wilhelm II Land, 

 McMurdo Bay, Adelie Land, Enderby Land, MacRobertson Land). 



Pyura discoveryi (Herdman) (Text-fig. 45; PI. IV, fig. 1) 

 Halocynthia discoveryi Herdman, 19 10, p. 9, pi. 4, figs. 6-12. 



Occurrence. St. 27: S. Georgia, 110 m. St. 42: S. Georgia, 120-204 m. St. 140: S.Georgia, 

 122-136 m. St. 144: S. Georgia, 155-178 m. St. 148: S. Georgia, 132-148 m. St. 152: S. Georgia, 

 245 m. St. 159: S. Georgia, 160 m. St. 160: S. Georgia, 177 m. St. 170: S. Shetlands, 342 m. 



