DESCRIPTION OF SPECIES 



125 



Pyura jacatrensis (Sluiter) (Text-fig. 51) 



Cynthia jacatretisis Sluiter, 1890, p. 331, pi. 1, figs. 8, 9. 

 For synonymy see Kott 1954, p. 127. 



Occurrence. St. 1563: Marion Island, S. Indian Ocean. 113-9901. 



External appearance. The single specimen is 3-2 cm. long and 2-2 cm. high, of an ovoid shape 

 and almost completely covered by sand, shell and debris. The siphons are visible externally as short 

 wide tubes more or less free of encrusting matter. 



Test. The test is not very thick, but is tough. Its inner surface is pale grey. On the lining of the 

 siphons there are slender pointed spines (Text-fig. 51 B, C) agreeing with those found by Kott (1954). 



Body wall. On the body wall the muscles which radiate from the siphons are quite numerous, and 

 regularly arranged (Text-fig. 51 A). The circular muscles are not numerous, except on and near the 

 siphons. 



1.0 an 



Text-fig. 51. Pyura jacatrensis (Sluiter) (St. 1563): A, specimen with test removed; B, spines from lining of oral siphon; 

 C, one of the spines at higher magnification ; D, oral tentacle ; E, dorsal tubercle ; F, posterior end of a branchial fold ; G, anus. 



Tentacles. There are sixteen oral tentacles (Text-fig. 51 D) of alternating sizes. The primary 

 branches are short and only very slightly divided. 



Dorsal tubercle. The opening of the dorsal tubercle is a small crescentic slit with the open interval 

 facing obliquely to the right and forward (Text-fig. 51 E). 



Branchial sac. Six sharply defined folds are present on each side of the branchial sac, with longi- 

 tudinal bars thus arranged: dorsal line 1 (14) 3 (16) 3 (16) 2 (17) 2 (15) 3 (n) 3 endostyle. 



There are about thirteen stigmata to each mesh on the flat parts between folds. The dorsal lamina is 

 represented by about forty narrow pointed languets. At the posterior end of each branchial fold the 

 longitudinal bars are prolonged as groups of slender processes (Text-fig. 51 F). 



