128
THE BIOLOGY O F EUPHAUSIIDS
300
in order to define the developmental pathways of any one species.
Einarsson (1945) has shown similar variation in the development of
Thysanoessa inermis and a detailed examination of the papers quoted
in Table I1 produces further examples of local variation. The factors
E. superba
-
WS 527
Clyde, April, 1957
Clyde,May, 1957
400
Clyde, 1963
400
300
Clyde, 1957
lLi0
Clyde,1926
60
311
Iceland
which produce this variation are as yet unknown. Availability of food
is probably important but other factors are no doubt also involved.
The course of development in the genus Euphausia varies from
species to species. The species are arranged in their recognized
groupings in this genus (Fig. 47 ; also see p. 326). Euphausia brevis,
FIG. 49. The frequencies of different larval forms i n the first and second furciliae of
Thysanoessa raschii (Einarsson, 1945 ; Mauchline, 1965a), Euphausia superba
(Frsser, 1936). Meganyctiphanes norvegica (Einarsson, 1945; Mauchline, 1959 ;
Soulier, 1965a). and Nyctiphanes australis (Sheard, 1953).