3,2 DISCOVERY REPORTS 



PREVIOUS WORK ON THE SPECIES 

 Since the original description by Holt and Tattersall (1906), based on a single male specimen taken 

 by the National Antarctic Expedition, E. triacantha has been described from the material taken by 

 many of the major expeditions to the Southern Ocean. In 1902 the Swedish Antarctic Expedition 

 took this species at four stations in the eastern south Atlantic. At one station in June Hansen (191 3, 

 p. 34) records 'numerous specimens' and also that the stages of development at another station in 

 April ranged 'from very young to full grown'. Hansen gives a fuller description than was possible 

 from the type specimen and includes an account of the copulatory organs. Zimmer (1914) records 

 five specimens taken by the Deutsche Sudpolar-Expedition in the Indian Ocean, and lUig (1930) 

 records four specimens taken by the Deutsche Tiefsee-Expedition. Tattersall (1924), in a survey of 

 the Subantarctic and Antarctic euphausiids, considered that E. triacantha was entirely a Subantarctic 

 species. The ' Norvegia ' Expedition 1927-8 and 1928-9 took six specimens, five females and one larva. 

 This larva, a second furcilia, was the first that had been taken and Rustad (1930) describes it in some 

 detail. The later ' Norvegia ' Expeditions, 1929-30 and 1930-1 , took fewer adults but provided material 

 for the description of the first, second and third calyptopes (Rustad, 1934). Ruud (1932), in an account 

 of the Euphausiidae taken on the whaling expedition of S.S. ' Vikingen' in 1929 30, mentions fifteen 

 specimens that were taken, and suggests that the species belongs to the warm deep water. He also 

 describes two metanauplii which he believes 'very probably belong to one of the two species, E.frigida 

 or E. triacantha '. 



Subsequent work has mainly been based upon material from the ' Discovery ' collections. Mackintosh 

 (1934), in his account of the distribution of the macroplankton in the neighbourhood of the Falkland 

 Island Dependencies, includes E. triacantha in the species which probably belong only to the Antarctic 

 water but which occasionally stray into Subantarctic water. He also points out that the numbers 

 taken in the surface show a marked diurnal variation. This diurnal variation was also observed by 

 Hardy and Gunther (1935) who note the almost complete absence of the species from the upper 

 200 m. during daylight hours and conclude that this is due to a diurnal vertical migration. They also 

 note that at times it was 'moderately abundant ' ofT the north and north-eastern coast of South Georgia 

 and that it was present at only one station in the region to the south and south-west of the island. 



In his account of the southern species of the genus Enphausia John (1936) gives a full description 

 of the adults and of the larvae from the second calyptopis upwards. He distinguishes seven furcilia 

 stages and gives length ranges for these and the calyptopis stages. From the examination of the 

 characteristics, mainly of the copulatory organs, of Hansens Group d (191 1), he shows this to be a 

 natural group and suggests that the four species, E. hanseni Zimmer, 191 5, E. spinifera Sars, 1885, 

 E. longirostris Hansen, 1908 and E. triacantha, represent stages in the colonization of the cold southern 

 water, E. hanseni being the most northern and E. triacantha the most southern species of the group. 

 Regarding the distribution he shows that E. triacantha occurs to the north of the northern limit of 

 the pack-ice and in a narrow belt of the Subantarctic. He also suggests that breeding takes place in 

 this narrower, Subantarctic, part of its range. 



While considering the vertical distribution of the Antarctic macroplankton Mackintosh (1937) 

 suggests that, in spite of the rather scanty material taken by the 70 cm. vertical nets, E. triacantha can 

 be included among those species that perform an energetic daily migration but no extensive annual 

 migration. He also points out that the limits of distribution of a species may be controlled by migration 

 between the northward moving surface water and the southward moving deep water. 



Other descriptions and references to the distribution of E. triacantha are included in Tattersall (1908, 

 1913) and Hansen (191 1); keys are to be found in Tattersall (1925), Rustad (1930) and Sheard (1953). 



