SALPA FUSIFORMIS CUVIER AND 

 RELATED SPECIES 



By P. Foxton 

 (Plates I-II and Text-figs, i-io) 



INTRODUCTION 



THIS paper represents the first part of a study of the salps of the Southern Ocean, and is a contribu- 

 tion to the National Institute of Oceanography's studies of the distribution of oceanic organisms 

 and the factors that govern them. 



Previous studies, which have described the distributions and Ufe-histories of species of Chaetognatha 

 (David, 1955, 1958) and Euphausiidae (Baker, 1959; Marr, in press) show that even in an area of 

 relatively simple oceanic circulation with well-defined water masses, such as the Southern Ocean, there 

 is more regional differentiation in plankton distribution than had hitherto been supposed. Further- 

 more, these regional differences become more apparent when it is possible to ascertain the range of 

 variation between species, subspecies and local races. 



The salps commend themselves to a special study because, apart from the work of Michael (19 18) 

 and Yount (1958), little attention has been paid to the relationship between their life-history and 

 their environment in spite of the fact that they were one of the earliest planktonic groups to be 

 described. In the Southern Ocean the salps are of especial interest because they occur at certain 

 seasons in dense concentrations or swarms and, as they are primarily herbivorous, must play an 

 important role in grazing down the phytoplankton, competing where distributions overlap, with such 

 other key herbivores as Euphausia superba. 



The common salp of the subantarctic and antarctic zones of the Southern Ocean has in the past 

 been assumed to be Salpa fiisiformis aspera, a variety or subspecies, characterized by a serrated test, 

 of the type S.fusiformis. Confusion in the literature and discrepancies between published descriptions 

 and specimens from the Southern Ocean made it necessary at the outset to examine in detail the 

 taxonomy of the salp common in our collections and to establish the validity or otherwise, not only 

 of previous identifications, but of aS". fusiformis aspera as a subspecies, form or extreme variant of 

 S. fusiformis. 



Fortunately a large collection of material was available for study mainly from the Southern Ocean 

 but also to a lesser extent from the Southern Indian, North Atlantic and South Atlantic Oceans. 

 I have also, by the kindness of workers in other laboratories, been able to extend the geographical 

 range of specimens examined into areas not represented in the plankton collections of the National 

 Institute of Oceanography. 



The results of this study show that the differences between S . fusiformis and the variety S.fusiformis 

 aspera are greater than had been previously supposed. Within what I shall refer to as the ' fusiformis 

 group ' there has been a confusion of four species, three of these being hitherto variously known as 

 S. fusiformis aspera. Morphological differences and features of geographical distribution allow the 

 four species S. fusiformis, S. aspera, S. thompsoni and S. gerlachei to be recognized. Two of these 

 species, S. thompsoni and S. gerlachei, are limited in their distribution to the Southern Ocean and it is 

 with the ecology of these that a later paper will be primarily concerned. It was felt, however, that it 



