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PACIFIC SCIENCE, VoL XIII, October, 1959 
cies (Fig. 9) that species may be present, in 
moderate numbers, up to midmorning and 
from midafternoon on. However, all species, 
except P. gracilipes and a few P. australis, were 
absent or rarely captured in hauls between 
these times. 
The common species of amphipod, by 
their irregular, spasmodic occurrences, sug- 
gest that in New Zealand waters, as elsewhere, 
distribution is affected by patchiness, and 
that a degree of independence of known con- 
trolling factors in the vertical movements of 
species is probable. Interpretations of distri- 
butions of species may thus be conditioned 
by the presence or absence of specimens as a 
result of (undetected) irregularities in their 
vertical movements. 
Parathemisto species 
Hurley (1955) analyses the complex taxon- 
omy of P. gaudkhaudii, P. australis, and P. 
gracilipes. He points out (p. 161) that ”al- 
though the three groups of Parathemisto here 
recorded from New Zealand can be separated 
quite distinctly by the pectination of the 
uropods, the general facies and by ecological 
preferences and habits, it is still possible that 
they do not warrant specific status. . ...” He 
briefly discusses the ecological data available 
to him from preliminary studies, and their 
relationships to the systematic positions of 
the species. As a result of the more detailed 
treatment possible in the present study, Hur- 
ley’s general statement can now be amplified 
and modified. 
In the preliminary studies it appeared that 
the habitats of P. australis and P. gracilipes, 
although overlapping, were separable respec- 
tively into shallow inshore waters and waters 
of intermediate depth. However, the T-S-P 
diagram (Fig. 4) shows that they occur at 
similar temperatures and salinities frequently 
at the same stations, in the warm coastal and 
mixed waters. In contrast, P. gaudichaudii in- 
habits colder water originating in the sub- 
antarctic, although it is able to penetrate into 
the inshore waters. Thus, for the area in ques- 
tion, there appear to be environmental pref- 
erences between P. gaudichaudii on the one 
hand and P. gracilipes and P. australis on the 
other, but not between P. gracilipes and P. 
australis, which facts are well demonstrated in 
the T-S-P diagrams (Figs. 3, 4). 
The variations in the diurnal patterns of 
the three species provide further evidence to- 
ward distinguishing between P. gaudichaudii 
and P. australis-P. gracilipes. P. gaudichaudii is 
rarely taken at the surface during daylight, 
but P. gracilipes and P. australis may be com- 
mon (Figs. 8, 9)= There is a double peak 
of numbers for P. gaudichaudii during dark- 
ness; both P. australis and P. gracilipes occur 
in large numbers at one and the same time. 
Further, the curve of diurnal variation for P. 
gracilipes closely parallels that for P. australis, 
indicating similar reactions to changing con- 
ditions (Fig. 9). Other similarities between 
P, gracilipes and P. australis are apparent in 
their relations to depth of water, and in the 
increases and decreases in numbers during 
January through March (Fig. 7). P. gaudi- 
chaudii differs considerably on these two 
points. 
Ecologically, it would appear that Parathe- 
misto gaudichaudii is separable as a distinct 
species from P. australis and P. gracilipes. 
However, an ecological distinction between 
P. australis and P. gracilipes in the New Zea- 
land area cannot be substantiated because of 
their closely parallel diurnal behaviour and 
similar distribution. These points are prob- 
ably not of sufficient moment to make P. 
gracilipes and P. australis conspecific, espe- 
cially as Hurley states the two forms are 
readily separable by their general facies. Their 
previous distributional records, too, indicate 
that the former is an oceanic, and the latter a 
coastal species. Although such markedly dif- 
ferent distributions should be reflected in 
their relationships to water masses in T-S-P 
diagram, this is not so. Thus the ecology of 
P. gracilipes and P. australis does little to assist 
in clarifying their systematic positions. On 
balance, it seems, however, that some taxo- 
