DESCRIPTION OF SPECIES 31 



diagnostic features. The anus is placed about half way along the branchial sac, opposite the 8th or 

 9th row of stigmata in zooids with 16 rows. It has two lobes. 



Gonads. Mature zooids generally have both ovary (ov.) and testis (t.). The ovary has a few ova of 

 various sizes and is situated immediately below the intestinal loop. The testis follicles form a long 

 series extending down the post-abdomen. In several colonies, mature zooids had the sperm duct 

 convoluted opposite and just below the intestinal loop (s.d.c). This is not the result of abdominal 

 contraction and the increased length of sperm duct may serve as a reservoir for sperm. 



Larva (Text-fig. 2 A 1 ). The variations in length of the larvae are shown in Table 4. 



Table 4 



All the colonies with these larvae were obtained from the Falkland Islands and the Patagonian Shelf. 

 There is no correlation between length of the larva and the month of the year. The larva is charac- 

 terized by the rather rounded and robust appearance of the trunk, the widely spaced papillae (p.), 

 and the four lateral ampullae on each side, each with a rounded swelling near the base (Fig. 2 A 1 , 

 a.sw.). 



Biology. The breeding season is indicated in Table 5 which shows the number of colonies examined 

 in each month in which the species was taken, and also the number of these colonies containing larvae. 



Table 5 



Month May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. 



No. of colonies examined 3 3 3 o o 4 7 36 12 8 14 15 



No. of colonies with larvae 000000000 1103 



When allowance is made for the small number of colonies collected between May and September 

 owing to the difficulty of working during the winter months, it is still evident that the breeding season 

 is limited to a short period in the southern summer and autumn, mainly the months of February, 

 March and April. 



Between one and seven larvae were found in the atrial cavity of zooids in different colonies. The 

 zooids with only one larva were smaller than those with several larvae. 



An examination of the colonies gives some picture of the annual cycle of growth and reproduction 

 in the species. In December most colonies have well-developed zooids but few have acquired gonads. 

 During the next three months the development of gonads takes place and few colonies were then found 

 which lacked gonads. Breeding follows with the greatest production of larvae in March. Subse- 

 quently, the gonads disappear and all the colonies collected in July had de-differentiated zooids 

 representing the normal post-breeding or overwintering condition in species of Aplidium. 



Remarks. It is difficult to be certain that all the suggested synonyms for this species are reliable, 

 and that all records under the name A.fuegiense refer to the same species. Of the reported occurrences 

 in the West Antarctic, those from Mac Robertson Land and Enderby Land (Kott, 1954) may not refer 

 to the present species. The colony and zooid described by Kott agree quite well with the specimens 

 from the Magellan region, but the number of folds on the wall of the stomach (8) is rather high. The 

 main difference, however, is the size of the larva, which Kott says is twice that of A. caeruleum 

 (Sluiter). The larva of the latter species is, according to Kott's scale drawing, about 1 mm. from the 

 end of the papillae to the base of the tail, which means that the larvae from MacRobertson Land and 

 Enderby Land were about 2 mm. in length. This is a very large larva indeed, and is between two and 



