136 DISCOVERY REPORTS 



Molgula setigera Arnback f. marioni n. (Text-fig. 58 E-G) 



Diagnosis of form. Differs from the typical form of the species in (1) opening of dorsal tubercle 

 a simple longitudinal oval slit, (2) long bristle-like hairs of test confined to region of siphons, and 

 (3) oviduct turned down ventrally. 



Occurrence. St. 1563: Marion Island, ioi-io6m. 



External appearance. The single specimen which is almost completely covered with sand and 

 fragments of shell is about i-6 cm. long. Two prominent groups of bristles, up to 6 mm. long, mark the 

 positions of the siphons. Elsewhere the body has a covering of very much more slender and flexible 

 test hairs. 



Tentacles. There are sixteen bi-pinnate tentacles of various sizes. 



Dorsal tubercle. The dorsal tubercle has a longitudinal oval opening (Text-fig. 58 F), quite 

 unlike that of the type specimens of M. setigera. 



Branchial sac. The seven folds on each side of the branchial sac have each from three to ten 

 longitudinal bars, the smallest number being on the most ventral fold. There are no bars between 

 folds. 



Gut. No differences were seen between the gut of f. marioni and f. georgiana. 



Gonads. The gonads have the same structure as in the typical form but differ in the downward bend 

 of the short oviduct, which is directed ventrally away from the atrial siphon (Text-fig. 58 G, od,). 



Remarks. This specimen is clearly related to the specimens from South Georgia representing 

 f. georgiana and the typical form of the species from Falkland Islands. But just as clearly it differs, 

 and the degree of difference is best recognized by placing the specimen in a separate form, f. marioni. 



If my interpretation of the ' Discovery ' material is right M. setigera presents an interesting case of 

 a species breaking up into separate populations, each inhabiting its own restricted area, and each 

 having slight but constant anatomical differences. Working with preserved material, it is impossible 

 to say whether these isolated populations, in the areas of Falkland Islands, South Georgia and Marion 

 Island respectively, have yet attained complete genetic, as well as geographical, isolation. If it could 

 be shown that they have, then the populations would have to be recognized as separate species, 

 instead of forms. 



M. setigera, it has been suggested (van Name, 1945), might prove to be synonymous with M. kop- 

 hameli Michaelsen, from the Strait of Magellan. The two species are similar but the complete absence 

 of bristles in M. kophameli does not support the suggestion. 



I believe that Kott's (1954) record of M. setigera from Enderby Land probably refers to a different 

 species. These Antarctic specimens have, judging from Kott's account, certain features which do not 

 agree with M. setigera. The position of the gonads seems to be different, since they diverge from the 

 intestinal loop and the renal sac, whereas in M. setigera they are close and parallel to those organs. 

 Also it is not clear if stiff bristles are present on the test. 



Distribution (of species including forms). Subantarctic (Falkland Islands, Marion Island), 

 Antarctic (South Georgia). 



Molgula sabulosa (Quoy & Gaimard) (Text-fig. 59) 



Ascidia sabulosa Quoy & Gaimard, 1834, p. 613, pi. 91, figs. 19-22. 

 Molgula forbesi Herdman, 1881, p. 236. 

 Molgula sabulosa Kott, 1952, p. 298, figs. 166-8. 



Occurrence. St. 1686: Victoria, Australia, o m. 



External appearance. There is only one specimen, and this measures 1 by 1 cm. The body is 





