ON THE SYSTEMATIC STATUS OF GLACIALIS, AND CALANUS HELGOLANDICUS

BY

W. A. JASCHNOV Moscow State University, Biological Faculty, Moscow-234,U.S.S.R.

In the Northern Atlantic, the adjacent seas and the Polar Basin three related species of Calanus are widespread: the arctic Calanus glaciali.r Jaschnov, the boreal Calanu.r finmarchicu.r (Gunnerus) and the subtropical Calanus helgolandicu.r (Claus) differing from one another in their morphology, ecology and distribution. The most important taxonomic characters of these species are body length, the curvature of the toothed border of the coxopodites of the fifth legs of females and the structure of these legs of males ( Jaschnov, 1 95 5 ) .

The validity of these species is admitted by the majority of investigators. Their distribution in the seas of the Northern Hemisphere has lately been studied ( Jaschnov, 1970).

Some researchers, however, take a different viewpoint. Thus Aurich (1966) considers all the three species to be geographical races of a single plastic species, while Matthews (1967) admitting the validity of C. f inmarchicu.r and C. helgo- landicu.r, regards C. glaciali.r as a subspecies of C. f inmarchicu.r. Both authors note the occurrence of forms with intermediate characters.

In a region inhabited by two related species individuals from different popu- lations performing diurnal and seasonal vertical migrations can occur in the same water layers. This favours the appearance of hybrid forms. Therefore the taxonomic characters of these species ought to be studied in those populations in which other related species are entirely absent. Just such populations were used in our study. Attention was given mainly to the differences between C. glaciali.r and C. finmar- chictis, but for comparative purposes the third species, C. helgolandicu.r, was also investigated.

Collections of C. finmarchicu.r were taken in July 1959 in the southern part of the , to the north of the Faeroe Islands, between 63 and 64°N, and 7 and 3°W. This population may be regarded as endemic in the Norwegian Sea where it occurs in the region of a cyclonic gyral ( Jaschnov, 1970). Collections of C. glaciali.r were taken in October 1961 in the White Sea, in the open part of 280 the Kandalaksha Bay. An endemic population of C. glacialis has existed in the White Sea since the Glacial period, when, owing to the penetration of the warm North Cape Current into the southern part of the , it was cut off from the main range of the species (Jaschnov, 1958). Collections of C. helgolandlcu-f were taken in the autumn months of 1957 and 1959 in the central part of the North Sea. The material was investigated in two directions. First total body length was determined, as well as the length of the anterior division of the body (cephalo- thorax, according to Jespersen, 1939, and metasome, according to Matthews, 1967), and, secondly, the value of the curvature of the toothed border of the coxopodites of the fifth legs of females was determined for each size-group.

Fig. 1. Length measurements of the anterior division of the body (fore-body) of adult females of Calanus finmarchicus (C.f.) from the southern part of the Norwegian Sea (350 specimens), Calanus helgolandicus (C.h.) from the North Sea (150 specimens) and CalanuJ glacialis (C.g.) from the White Sea (350 specimens).

The measurements of the length of the anterior division of the body (fore- body) of the adult females of all the three species are given in fig. 1. All the curves obtained are in good agreement with the normal curves, the ranges of variations are small. Analogous curves were also obtained for other species of northern . Jespersen (1939) gives such curves for , Pareuchaeta norvegica, P. glaciali.r, Metridia longa, and, in particular, for popu- lation of C. f inmarchicu.r in the Irminger Sea ``outside the East Greenland Polar Current". We have obtained similar curves for populations of C. finmarchicus carried by the North Cape Current into the south-western part of the Barents Sea,