DESCRIPTION OF SPECIES 25 



merits recognition as anything more than a rather indefinitely distinguished subgenus or section of 

 Aplidium Savigny', although it is 'universally adopted in all books on ascidians' (p. 30). 



Berrill (1950) pointed out the difficulties involved in using van Name's list of diagnostic characters, 

 and concluded that 'the situation is clearly absurd'. He adopted Aplidium as the comprehensive 

 genus, with Amaroucium as a subgenus. 



Using van Name's list of characters, I have compared forty species variously assigned to Aplidium 

 and Amaroucium, taking details from published accounts. An additional character included in the 

 comparison was the position of the anus relative to the rows of stigmata (Tokioka, 1953). With regard 

 to this last character I find that, although in some species the anus is situated opposite the 4th row of 

 stigmata, and in others opposite the 7th to 10th, yet the ratio of rows of stigmata anterior to anus to 

 rows of stigmata posterior to anus gives no clear separation of species into two groups. The two 

 characters which might be used to separate Aplidium and Amaroucium are (1) the arrangement of the 



Hartmeyer (1923-4) 



Harant & Vernieres (1933) 

 Huus (1937) 



van Name (1945) 



Table 1 



Aplidium 



Atrial siphon with or without languet 

 Testis follicles in a bunch 



Atrial languet absent 



Atrial opening with or without languet 

 Stomach longitudinally folded 

 Post-abdomen relatively short 

 Testes in a bunch or cluster 



Colony sessile by a broad base 

 Zooids rather stout, with few rows of 

 stigmata 

 Short post-abdomen 



Stomach with a few deep longitudinal folds 

 Atrial opening well back on dorsal side 

 Testes in a compact mass 



Amaroucium 



Atrial siphon always with languet 

 Testis follicles more or less regularly 

 arranged along sperm duct 



Atrial languet present 



Atrial opening with long languet 

 Stomach longitudinally folded 

 Post-abdomen long 



Testis follicles biserially arranged along 

 sperm duct 



Colony massive or capitate 



Zooids large with many rows of stigmata 



Long post-abdomen 



Stomach with distinct longitudinal plications 

 Atrial opening well forward 

 Testes serially arranged along the sperm 

 duct 



testes, and (2) the length of the post-abdomen. The first of these characters is undoubtedly influenced 

 by the second, a short post-abdomen tending to produce a bunching of the testis follicles, but the 

 length of the post-abdomen is itself an unsatisfactory character for generic distinction, as it varies 

 greatly during the annual cycle of the zooids. 



Another result of the shortening of the post-abdomen has been the development in Aplidium 

 pallidum (Verrill) of a type of budding shown by Brien (1925) to involve division of the stomach. 

 Should this feature be found to occur in other species, it might serve as a diagnostic character of 

 Aplidium, but as so far it has been studied only in A. pallidum, such a course is not at present 

 practicable. 



The above considerations lead me to believe that there is no generic distinction to be made within 

 the group, and I therefore agree with Berrill (1950) and Kott (1954) in adopting for all species the 

 generic name Aplidium, which has priority over Amaroucium. 



Aplidium circumvolutum (Sluiter) (Text-fig. 1; PI. I, fig. 1) 



Psammaplidium circumvolutum Sluiter, 1900, p. 14, pi. 1, fig. 7; pi. 3, fig. 1. 



Amaroucium circumvolutum Michaelsen, 1924, p. 383. 



Amaroucium circumvolutum var. kerguelenense Peres, 1952, pp. 213-15, figs. 1, 2. 



