DESCRIPTION OF SPECIES 33 



usual measurement of the thorax and abdomen together, but one of the colonies from the ' Challenger ' 

 collection which I have examined has well-expanded zooids with thorax 3-5 mm., abdomen 2-0 mm. 

 and post-abdomen 4-0 mm. 



Thorax. The oral siphon is 6-lobed and the atrial siphon has a simple or 3-cleft languet. The 

 branchial sac has from nine to fifteen rows of stigmata. 



Gut. The stomach has from ten to sixteen longitudinal folds, generally from twelve to fifteen. One 

 or two of the folds often extend only part of the length of the stomach. The anus has two distinct lips. 

 It is situated opposite the 8th row of stigmata in zooids with fifteen or sixteen rows. 



Larva (Text-fig. 2B 1 ). The larva of this species has not been described. It ranges from 0-58 to 

 070 mm. in length, measured from the end of the papillae to the base of the tail. The trunk is rather 

 deep and stout. The most characteristic feature of the larva is the presence of many small apparently 

 isolated vesicles (v.) arranged in a semicircle round the anterior end of the trunk. The three anterior 

 papillae are rather widely spaced and have slender stalks. There are no paired or median ampullae, 

 a feature unusual in species of Aplidium. Both ocellus and otolith are present. There are up to ten 

 larvae in the atrial cavity of breeding zooids. 



Remarks. Herdman (1886) pointed out that this species somewhat resembles A. fuegiense in 

 external appearance, and Hartmeyer (191 1, 1912) also regarded the species as similar. Van Name 

 (1945) stated that they are 'very likely synonymous'. I have examined many specimens of both 

 species, including thirteen colonies of Herdman's type material of A. variabile, kindly lent by the 

 British Museum (Natural History). In my opinion the species are certainly separate, and reliable 

 distinctions are found in both zooids and larvae, as shown in Table 6. 



Table 6 

 Stomach Larva 



A. fuegiense 5 or 6 undivided folds Trunk 0-66-0-90 mm. ; paired club-like anterior 



ampullae; no small isolated vesicles 



A. variabile Usually 10-15 folds, a few of them divided Trunk 0-58-70 mm. ; no club-like anterior ampullae; 



or incomplete many small isolated vesicles 



With regard to these features, the stomach of A. fuegiense is very characteristic and I find that the 

 number of folds does not exceed six, even in the largest colonies with fully mature zooids. The 

 'Discovery' material, therefore, gives no confirmation of van Name's (1945) statement that the folds 

 on the stomach sometimes number at least eight or ten. In the type specimens of A. variabile the 

 zooids which I have examined show thirteen to fifteen folds, thus agreeing with Herdman's statement 

 and illustration. Hartmeyer (191 1) found fourteen folds, sometimes fewer, and later (1912) stated 

 that the number may be as low as six; he may have been confusing the two species. There is little 

 doubt, however, that the number is generally at least twelve, and Kott (1954) always found fourteen 

 or fifteen folds. 



Although there were embryos in one of the type specimens, no fully developed larvae were present, 

 and the larval description is based on ' Discovery ' specimens from the Patagonian Shelf. The larvae 

 of A. variabile and A. fuegiense cannot be confused. 



Apart from one record for the Chatham Islands (New Zealand) by Sluiter (1900), A. variabile has 

 previously been taken only from Kerguelen, where it seems to be fairly common. Michaelsen (1924) 

 was in some doubt whether to accept the record from New Zealand, and if we ignore it, the previous 

 records were confined to Kerguelen. The wide geographical separation of the previous and the new 

 localities is perhaps not surprising, when it is remembered that the latitude of Kerguelen Island and 



