326
THE BIOLOGY O F EUPHAUSIIDS
Pseudeuphausia. Two species, one of which extends to more
oceanic areas of the Indian Ocean, but otherwise restricted to more
coastal regions of the western Pacific where they live at temperatures lower than 1 5 O C a t 200 m depth.
Euphausia. This genus contains thirty-two species divided into
four groups, namely :
Group A. E . americana, E. eximia, E. krohnii, E. mutica,
E. brevis, E . diomedeae, E. recurva.
Group B. E . superba, E. vallentini, E. lucens, E. frigida,
E . paci$ca, E . nana, E. crystallorophias, E. tenera, E. similis,
E. similis var. armata.
Group C. E. mucronata, E . sibogae, E . distinguenda, E. lamelligera, E. gibba, E. gibboides, E. fallax, E. sanzoi, E. pseudogibba,
E . paragibba, E . hemigibba.
Group D. E . spinifera, E. hanseni, E. longirostris, E.
triacantha.
Group A : These seven species, with the exception of E. krohnii, are
all tropical or subtropical and live a t daytime depths of 200 to 400 m.
The species are scattered geographically, only E. mutica, E. brevis and
E. recurva being widely distributed. Group B: Seven of these ten species
have circumpolar distributions in the Antarctic south of 4 0 ' 5 while
E. tenera is widely distributed in equatorial regions; E. paci$ca and
E. nana are restricted to the North Pacific. Group C: All of these
eleven species are tropical or subtropical; two of them are widely
distributed, two present only in the Indian and Pacific Oceans, five only
in the Pacific; E . gibboides occurs in the Pacific and Atlantic Oceans
but according to Brinton (1962a) probably does not occur in the Indian
Ocean or Red Sea where it has been confused with E. sanzoi, but
confirmation of the distributions of these two species is required.
Group D : This group contains three circumpolar species in the Antarctic
and E. hanseni which lives off the Atlantic coast of Africa. Thus, in
the genus Euphausia, twenty of the species are restricted to tropical
and subtropical regions, ten are circumpolar south of about 40°S,
E. krohnii lives in the temperate Atlantic and E. pacijca in the North
Pacific.
Tessarabrachion. The only species in this genus is T . oculatum which
is confined to the North Pacific.
Thysanohsa. Three of the ten species are confined to the North
Pacific, one to the North Atlantic, two to both these areas while a
further two are circumpolar in the Antarctic and two bipolar in the
Atlantic and Pacific and also occur in the Indian Ocean. None of these
THE BIOLOGY O F EUPHAUSIIDS
Pseudeuphausia. Two species, one of which extends to more
oceanic areas of the Indian Ocean, but otherwise restricted to more
coastal regions of the western Pacific where they live at temperatures lower than 1 5 O C a t 200 m depth.
Euphausia. This genus contains thirty-two species divided into
four groups, namely :
Group A. E . americana, E. eximia, E. krohnii, E. mutica,
E. brevis, E . diomedeae, E. recurva.
Group B. E . superba, E. vallentini, E. lucens, E. frigida,
E . paci$ca, E . nana, E. crystallorophias, E. tenera, E. similis,
E. similis var. armata.
Group C. E. mucronata, E . sibogae, E . distinguenda, E. lamelligera, E. gibba, E. gibboides, E. fallax, E. sanzoi, E. pseudogibba,
E . paragibba, E . hemigibba.
Group D. E . spinifera, E. hanseni, E. longirostris, E.
triacantha.
Group A : These seven species, with the exception of E. krohnii, are
all tropical or subtropical and live a t daytime depths of 200 to 400 m.
The species are scattered geographically, only E. mutica, E. brevis and
E. recurva being widely distributed. Group B: Seven of these ten species
have circumpolar distributions in the Antarctic south of 4 0 ' 5 while
E. tenera is widely distributed in equatorial regions; E. paci$ca and
E. nana are restricted to the North Pacific. Group C: All of these
eleven species are tropical or subtropical; two of them are widely
distributed, two present only in the Indian and Pacific Oceans, five only
in the Pacific; E . gibboides occurs in the Pacific and Atlantic Oceans
but according to Brinton (1962a) probably does not occur in the Indian
Ocean or Red Sea where it has been confused with E. sanzoi, but
confirmation of the distributions of these two species is required.
Group D : This group contains three circumpolar species in the Antarctic
and E. hanseni which lives off the Atlantic coast of Africa. Thus, in
the genus Euphausia, twenty of the species are restricted to tropical
and subtropical regions, ten are circumpolar south of about 40°S,
E. krohnii lives in the temperate Atlantic and E. pacijca in the North
Pacific.
Tessarabrachion. The only species in this genus is T . oculatum which
is confined to the North Pacific.
Thysanohsa. Three of the ten species are confined to the North
Pacific, one to the North Atlantic, two to both these areas while a
further two are circumpolar in the Antarctic and two bipolar in the
Atlantic and Pacific and also occur in the Indian Ocean. None of these