86 DISCOVERY REPORTS 



contains muscles of the body wall and is not homologous with the vascular process which occupies a 

 similar position in the related Diazona. In Diazona the vascular process has a mesenchymatous 

 septum and no extension of the epicardium. 



Gonads (Text-fig. 25 E). Specimens collected in July (St. WS 243, Patagonian Shelf), and March 

 (St. 371, South Sandwich Islands) had well-developed gonads consisting of bunched testis follicles 

 (t.) at the lower end of the intestinal loop, and an elongated ovary (ov.) below the testis. 



Larva (Text-fig. 25 H). Two of the specimens carry larvae. One colony from the Patagonian Shelf 

 (St. WS 243), collected in July, has only three larvae in the zooids, and one colony from South 

 Georgia (St. 144) collected in January, has many larvae in each breeding zooid. Only the latter 



Species or 

 material 



T. antarcticum 

 T. speciosum 

 T. weddelli 



' Discovery ' 



St. 144 



(4 colonies) 

 ' Discovery ' 



St. WS 27 



(18 colonies) 



Height of 

 colony 

 (cm.) 



Up to 2 



•6-27 



1-6-s-o 



3-o. 3'5 



'Discovery' 



St. 371 



(2 colonies) 

 ' Discovery ' 



St. WS 243 



(1 colony) 

 ' Discovery ' 



St. WS 841 



(piece of i colony) 

 'Discovery' 4-5, 4-0 



St. 160 



(2 colonies) 



4'5 



Piece, 

 7 by 9 



Length of 

 zooids 

 (mm.) 



Thorax 2, 



abdomen 2-75 

 Thorax 4-5, 



abdomen 7-8 

 Thorax 7-8, 



abdomen 7 

 Thorax 3-5-5-0, 



abdomen 3-0- 



5-5 

 Thorax 2-0-6-0, 

 abdomen 3-0- 

 7-0 



Thorax 6-7, 

 abdomen 7-9 



Thorax 4, 

 abdomen 5 



Thorax 3, 

 abdomen 3 



Thorax 5-6, 

 abdomen 3-5 



Table 25 



Thoracic 

 muscles 



7 or 8 



Numerous 

 (about 11?) 

 9 or 10 



6-8 



7-12 



7-10 



6-8 



Branchial 

 papillae 



Tall; processes 

 long 



Flattened; pro- 

 cesses short 



Flattened; pro- 

 cesses short 



Short; processes 

 quite long 



Short with short 

 processes or 

 long with long 

 processes 



Long; processes 

 long 



Long; processes 

 long 



Short; processes 

 short 



Short; processes 

 short 



Stomach 

 folds 



Sinuous and 



narrow 

 About 17, 



slightly sinuous 

 14, straight 



17-19; mostly 

 straight 



12-18, mostly 

 straight, but 

 some sinuous in 

 some zooids 



12-16, straight 



Apparently 

 smooth 



10-12 



15 or 16 



Distribution or 

 occurrence 



E. and W. 



Antarctic 



Kerguelen 



W. Antarctic 



S. Georgia 



S. Georgia 



S. Sandwich Is. 

 Patagonian Shelf 

 Patagonian Shelf 

 Shag Rocks 



specimen has fully developed larvae. These measured about 0-55 mm. from the end of the papillae to 

 the base of the tail. There are two short dorsal papillae (d.p.) placed close together, and one short 

 ventral papilla (p.p.), the three arranged to form a triangle. The trunk is deep and rounded. Within 

 the cerebral vesicle the black otolith projects from the floor, but there is no trace of a pigmented 

 ocellus. 



Remarks. Three species of Tylobranchion have been described from southern waters, T. speciosum, 

 Herdman, T. antarcticum Herdman, and T. zveddelli Arnback. Van Name (1945) doubted whether 

 they are distinct, and Kott (1954), after examining material from the B.A.N. Z. Antarctic Research 

 Expedition of 1929-31 decided that they all represent one species. But Arnback (1950) still maintained 

 their separation. I have to record, however, that in her personal notes, to which I have had access, 

 she seemed to have found less clear distinctions between the species represented in the 'Discovery' 

 collections. The characters shown in Table 25 include those used by Arnback to separate the three 

 species. They show such a degree of overlapping that I am accepting Kott's (1954) view of the identity 

 of the species, the name T. speciosum having priority. 



