11. ECOLOGY OF DISTRIBUTION
327
species occurs in tropical or subtropical regions with the possible exception of T . parva.
Nematoscelis. All seven species occur in tropical or subtropical
regions, three being present in the Atlantic, Pacific and Indian Oceans
and N . atlantica will also probably be found in the Indian Ocean through
future observation. Two species are restricted to the Pacific, and one
to the Pacific and Atlantic Oceans.
Nematobrachion. The three species in this genus are tropical or
subtropical, two are widely distributed while the rarer N . sexspinosum
has, so far, only been recorded from the Pacific and Atlantic Oceans
although Baker (personal communication) considers he found three
juveniles in his transect 90"E 0"-37"S.
Stylocheiron. These eleven species all occur in tropical or subtropical
regions but S. maximum has been found between 60"N and 60"s. Eight
of them occur in all three oceans, and future sampling may show that
8. robustum is not confined to the Pacific and Atlantic Oceans. One
species, S. insulare, is restricted to the Pacific and has been found once
in the Atlantic. S. indicum has so far only been recognized in the Indian
Ocean.
Thus, species in the genera Bentheuphausia, Thysanopoda, Nyctiphanes, Pseudeuphausia, Nematoscelis, Nematobrachion, and Stylocheiron
-forty species in all-live predominantly in tropical and subtropical
regions along with twenty-two species of the genus Euphausia.
Thysanopoda acutifrons, Meganyctiphanes norvegica, Tessarabrachion
oculatum, ten species of the genus Euphausia, and all species of the genus
Thysanoessa-twenty-three species in all-live in either the northern
or the southern regions of the oceans.
The species can be further grouped according to the extent of their
longitudinal distributions :
(a) Species which are widely distributed, that is occur in the Atlantic,
Pacific and Indian Oceans. It is probable that Nematoscelis atlantica
which is difficult to separate from the closely similar N . microps, and
the rare deep sea Thysanopoda egregia and T . spinicaudata are also in
this group.
Bentheuphausia amblyops; Thysanopoda monacantha, T . cristata,
T. tricuspidata, T . aequalislT. subaequalis, T . obtusifrons, T . pectinata,
T . orientalis, T . acutifrons, T . cornuta, T . egregia(?), T . spinicaudata (2);
Euphausia mutica, E. brevis, E . recurva, E . superba, E . vallentini, E .
lucens, E . frigida, E. crystallorophias, E. tenera, E . similis, E . similis
var. armata, E . gibboides ( 1 ) , E . pseudogibba, E. hemigibba, E . spinifera,
E . longirostris, E . triacantha; Thysanoessa parva, T . gregaria, T .
vicina, T . macrura; Nematoscelis megalops, N . tenella, N . micropslN.
327
species occurs in tropical or subtropical regions with the possible exception of T . parva.
Nematoscelis. All seven species occur in tropical or subtropical
regions, three being present in the Atlantic, Pacific and Indian Oceans
and N . atlantica will also probably be found in the Indian Ocean through
future observation. Two species are restricted to the Pacific, and one
to the Pacific and Atlantic Oceans.
Nematobrachion. The three species in this genus are tropical or
subtropical, two are widely distributed while the rarer N . sexspinosum
has, so far, only been recorded from the Pacific and Atlantic Oceans
although Baker (personal communication) considers he found three
juveniles in his transect 90"E 0"-37"S.
Stylocheiron. These eleven species all occur in tropical or subtropical
regions but S. maximum has been found between 60"N and 60"s. Eight
of them occur in all three oceans, and future sampling may show that
8. robustum is not confined to the Pacific and Atlantic Oceans. One
species, S. insulare, is restricted to the Pacific and has been found once
in the Atlantic. S. indicum has so far only been recognized in the Indian
Ocean.
Thus, species in the genera Bentheuphausia, Thysanopoda, Nyctiphanes, Pseudeuphausia, Nematoscelis, Nematobrachion, and Stylocheiron
-forty species in all-live predominantly in tropical and subtropical
regions along with twenty-two species of the genus Euphausia.
Thysanopoda acutifrons, Meganyctiphanes norvegica, Tessarabrachion
oculatum, ten species of the genus Euphausia, and all species of the genus
Thysanoessa-twenty-three species in all-live in either the northern
or the southern regions of the oceans.
The species can be further grouped according to the extent of their
longitudinal distributions :
(a) Species which are widely distributed, that is occur in the Atlantic,
Pacific and Indian Oceans. It is probable that Nematoscelis atlantica
which is difficult to separate from the closely similar N . microps, and
the rare deep sea Thysanopoda egregia and T . spinicaudata are also in
this group.
Bentheuphausia amblyops; Thysanopoda monacantha, T . cristata,
T. tricuspidata, T . aequalislT. subaequalis, T . obtusifrons, T . pectinata,
T . orientalis, T . acutifrons, T . cornuta, T . egregia(?), T . spinicaudata (2);
Euphausia mutica, E. brevis, E . recurva, E . superba, E . vallentini, E .
lucens, E . frigida, E. crystallorophias, E. tenera, E . similis, E . similis
var. armata, E . gibboides ( 1 ) , E . pseudogibba, E. hemigibba, E . spinifera,
E . longirostris, E . triacantha; Thysanoessa parva, T . gregaria, T .
vicina, T . macrura; Nematoscelis megalops, N . tenella, N . micropslN.