SAGITTA GAZELLAE 245 



S. gazellae was originally described in 1909 by Ritter-Zahony from Subantarctic material taken by 

 the 'Gazelle' expedition (1874-76). Unfortunately this description was incomplete, in that the fins 

 were not observed owing to the long preservation of the specimens in alcohol ; from other features the 

 species was thought to be nearest to S. hexaptera. Ritter-Zahony did not consider possible confusion 

 with S. lyra until later when he examined the well-preserved collection of the ' Gauss '. The specimens 

 from this collection showed that the lateral fins were set on lateral fields as in S. lyra and that there was 

 little resemblance to S. hexaptera. Ritter-Zahony therefore redescribed the species in 191 1, but the 

 description was still inadequate, owing partly to the fact that his collections contained no sexually 

 mature individuals, and partly to an overlap in the tail segment percentages of 5. gazellae and S. lyra, 

 as shown in his tables on pages 9 and 1 1 . 



Germain (1913) and Jameson (1914) both recognized and recorded S. gazellae from Antarctic waters, 

 though neither the 'Pourquoi pas?' nor the 'Scotia' collections contained any mature individuals. 

 Michael (191 1), in a discussion on the species of chaetognaths not taken in the San Diego region, 

 drew attention to the shortcomings of Ritter-Zahony's original description of S. lyra and S. gazellae, 

 but, being unable to examine any specimens of 5. gazellae himself, was prepared to let it stand as 

 a separate species, and in a later publication (19 19) included it in his key. 



In 1 92 1 Johnston & Taylor published their report on the Chaetognatha of the Australasian 

 Antarctic Expedition in which they decided that S. gazellae was synonymous with S. lyra. 



Despite Johnston & Taylor's opinion, Burfield (1930) felt justified in retaining S. gazellae as a 

 separate species, although he pointed out that precise distinction was most difficult. 



In the report on the ' Deutschland ' collection, Bollmann (1934) also retained S. gazellae, but he 

 evidently had much difficulty in distinguishing it. 



Kuhl (1938) included S. gazellae in his key, but without special comment, and presumably regarded 

 Bollmann's view, the most up-to-date opinion at that time, as correct. 



The 'Meteor' must have taken specimens of S. gazellae, but Thiel (1938) has dealt with certain 

 species in groups, and has included S. maxima, S. lyra and S. gazellae in his ' S. maxima group ' and has 

 not therefore contributed to the problem of the synonymy. (Though these three species resemble one 

 another in many anatomical features, their distributions are dissimilar and thus his picture of distribu- 

 tion of the group is of little value.) 



This point in the history of S. gazellae is a most important one, for, up to 1939, most authors who 

 wrote about the species had examined and described specimens from areas in which (as I shall show 

 later) S. gazellae is found ; whereas subsequent authors with one partial exception have examined and 

 described specimens from areas in which S. gazellae is not found, and have in fact described variation 

 in 5. lyra Krohn. They have shown that certain forms of S. lyra resemble S. gazellae, and have claimed 

 that intermediate forms exist which link S. gazellae with S. lyra. I have been unable to find any such 

 intermediates in the Discovery collections. There is, however, a continuous series of intermediates 

 between the extremes of variation of S. lyra, and I believe that the incorrect assumption that 'the cold 

 water form of S. lyra Krohn is identical with S. gazellae Ritter-Zahony ' has been responsible for 

 much confusion. 



In 1939 Tokioka described certain specimens of S. lyra closely resembling S. gazellae, from 

 Japanese waters; these he called S. lyra "gazellae "-type to distinguish them from the typical S. lyra, 

 which he named S. lyra " lyra" -type. 



Thomson, in 1947, records the existence of both these forms in S.E. Australian waters and follows 

 Johnston & Taylor and Tokioka in regarding S. lyra "lyra"-type and S. gazellae Ritter-Zahony as 

 extremes of variation in one species; he regarded S. gazellae and the 'intermediate types' as S. lyra 

 "gazellae" -type. 



