DESCRIPTION OF SPECIES 89 



The third criterion, the presence or absence of intermediate papillae in the branchial sac, is also 

 an unreliable character. In A. translucida, Hartmeyer (1912) found that secondary papillae were 

 present in older specimens but not in younger ones. Arnback (1938) also noted that in A. translucida 

 these papillae exist in some parts of the branchial sac but not in others. 



For these reasons I regard A. plicata as very probably a synonym of A. translucida. 



Distribution. Antarctic (South Georgia), Subantarctic (Kerguelen). 



Ascidia challenged Herdman (Text-fig. 27) 



Ascidia challengeri Herdman, 1882, p. 102, pi. 30. 



Ascidia charcoti Sluiter, 1905, p. 471. 



Ascidia dispar Arnback, 1938, p. 48; text-fig. 11. 



Occurrence. St. 145: S. Georgia, 26-35 m. St. 156: S. Georgia, 200-236 m. St. 160: Shag 

 Rocks (S. Georgia), 177 m. St. 164: S. Orkneys, 24-36 m. St. 195: S. Shetlands, 391 m. St. 1652: 

 Ross Sea, 567 m. St. 1660: Ross Sea, 351 m. St. WS 27: S. Georgia, 107 m. St. MS 71 : S. Georgia, 

 110-60 m. B.G.L.E., 1934-7, Stella Creek. 



p.bd 



Text-fig. 27. Ascidia challengeri Herdman (St. 145): Oral tentacles. 



External appearance. The specimens range in length from 1-3 cm. to n-o cm., the largest being 

 from the Ross Sea. They vary from a regular oval and laterally flattened form to an irregular pear- 

 shaped form. The siphons are generally, but not always, inconspicuous, the oral one terminal and the 

 atrial about one-third of the body length from it. 



No. of tentacles 

 Dorsal lamina 



No. of longitudinal branchial bars 

 per side 



Intermediate branchial papillae 

 Branchial stigmata 



Table 27 



A. dispar 



About 50 



Extends far beyond oesophageal mouth 



40-50 



Absent 



Short and irregular 



A. challengeri 



Few, usually up to 20 



Scarcely extends beyond oesophageal mouth 



3 -32 



Usually present 

 Long and regular 



Remarks. Arnback (1938) described a new species A. dispar, based on a single specimen from South 

 Georgia. She recognized the strong similarity to A. challengeri, but gave as main distinctions those 

 shown in Table 27. 



Of these characters the ones which, judging by distinctions between other species of Ascidia, are 

 likely to be the most reliable are (1) the number of tentacles, (2) the number of longitudinal branchial 



