ii2 DISCOVERY REPORTS 



Branchial sac. The complete absence of branchial folds constitutes the most remarkable and 

 characteristic feature of the species. There are only four large longitudinal bars on each side of the 

 branchial sac. Plication of the branchial wall increases the surface area, as it does in several species of 

 Ascidia. 



Gut (Text-fig. 42B). Sluiter has already described the course of the gut, noting the longitudinal 

 position of the stomach and double intestinal loop. All the 'Discovery' specimens confirm his 

 description, but I find more folds on the wall of the stomach, about thirty-five even in a small specimen 

 instead of the twenty which he found, and the stomach sometimes lies obliquely or almost vertically. 

 The margin of the anus has about twelve distinct lobes. 



Gonads. In the type specimens Sluiter described one gonad on the left and two on the right, but 

 Kott (1954) found only one on each side. In the 'Discovery' material also there is a single gonad on 

 each side. The anterior part of each ovary (Text-fig. 42 C, ov.) is straight and the posterior part 

 variously bent. In the largest specimen the right gonad is distinctly curved upwards to form a U with 

 unequal limbs. Groups of testis follicles (t) are situated along the length of the ovaries, but are more 

 plentiful at their posterior ends and are sometimes confined to this region. 



Remarks. This is a species which has seldom been taken by expeditions, only Sluiter and Kott 

 having examined material so far as I know. 



Very few styelid ascidians, other than compound forms, have carried the reduction of branchial 

 folds, and even branchial bars, so far. I would point to the similarity between the present species 

 and the Arctic styelid species Pelonaia corrugata Goodsir & Forbes, which also has flat branchial 

 walls. The form of the gonads is another point of similarity, particularly in the specimen of S. insinu- 

 osa with a U-shaped gonad. Both are aberrant species of the family Styelidae, but it is doubtful 

 whether the resemblance is due to convergence or to close relationship. 



Distribution. Antarctic (South Shetlands, King George V Land; South Georgia). 



Styela magalhaensis Michaelsen (Text-fig. 43) 



Styela canopus var. magalhaensis Michaelsen, 1898, p. 367. 

 ?5. melincae Arnback, 1929, p. 2. 



Occurrence. ?St. 123: S. Georgia, 230-250 m. St. WS 776: Patagonian Shelf, 110-99 m. 



External appearance. The single specimen from St. WS 776 is of a squat conical shape with the 

 siphons forming low projections close together on the upper narrow side. Irregular rounded swellings 

 are present on the surface. The general colour is creamy grey. The length and height are both i-i cm. 



Test. The test, although tough, is not very thick. It is raised in irregular wart-like swellings. 



Body wall. Longitudinal and circular muscles are evenly spread over the rather thin body wall, 

 which is brown in the preserved state. 



Tentacles. There are about sixty-four of various sizes. 



Dorsal tubercle. The dorsal tubercle has a simple U-shaped opening facing forward. 



Branchial sac. Each side of the branchial sac is thrown into four quite distinct folds, with the 

 following distribution of longitudinal bars: dorsal line 4(14)4(15)6(12)5(13)4 endostyle. The 

 dorsal lamina is a simple membrane with a plain inrolled edge. 



Gut. Most of the gut lies in the lower part of the body. The oesophagus is curved, and the walls of 

 the long stomach have about twenty-four longitudinal folds. There is a very small pyloric caecum. 

 The first part of the intestine lies parallel to the stomach, and the rectum bends upwards towards the 

 atrial siphon. 



Gonads. One of the most characteristic features of this species is the form of the gonads (Text- 

 fig. 43 G). In ripe specimens these constitute two long tubular sinuous ovaries (ov.) on each side, with 



