11. EcoLoaY OF DISTRIBUTION
339
are common in the Bering Sea (Nemoto, 1962a). Thysanoessa raschii
and T . inermis penetrate north of the Bering Straits into the Arctic and
the southern limits of their distributions are immediately south of the
Aleutian Islands Chain. The northern limits of the distributions of the
other three species are north of the Aleutians but they are not common
there although they do occur in the southern half of the Bering Sea.
The horizontal and vertical distributions of the species are shown
diagrammatically in Fig. 126 which represents a section extending
southwards from the Bering Straits. ThysanoZssa inermis, T . raschii
and T . longipes are common in the Sea of Okhotsk while Euphausia
pacijica is very rare ; no other euphausiids live in this subarctic area.
Pacijlc (4O"N-4O0S)
Fifty-nine species are resident in this region but some of the subarctic
and subantarctic species are found south of 40"N and north of 40"s
respectively and so, as in the descriptions of the distributions of the
Atlantic species, these latitudinal limits are only approximate guides to
changing hydrographic regimes and changing euphausiid communities.
Transition zones between subarctic (and subantarctic) and central
Thysanopoda acutifrons; Euphuusia pacijica, E . gibboides;
waters
Thysanoessa gregaria; Nematoscelis dificilis, N . megalops.
Central waters of North and South Pacific
Thysanopoda aequalislT. subaequalis, T . obtusifrons; Euphausia
mutica, E. brevis, E . recurva, E . gibba, E . hemigibba; Nematoscelis
atlantica; Stytocheiron afine " Central Form ", S . suhmii.
Equatorial waters
Thysanopoda tricuspidata; Euphuusia diomedeae, E . tenera, E.
paragibba; Nematoscelis gracilis; Stylocheiron a$ine " W. Equat.
Form ", S. microphthalma.
Central and equatorial waters
Bentheuphausia amblyops; Thysanopoda monacuntha, T . orientalis, T . pectinata; Nematoscelis tenella, N . microps; Nematobrachion
Jlexipes, N . boopis; Xtylocheiron carinatum, 8. elongatum, S. longicorne, X . abbreviatum, S. maximum.
Localized distribution
Nyctiphanes australis, N . simplex; Pseudeuphausia latifrons,
P. sinica; Euphausia eximia, E . nana, E . similis, E. mucronata,
E . sibogae, E. distinguenda, E . lamelligera, E. fallax, E. pseudogibba;
Thysanoessa spinifera; Nematoscelis lobata; Stylocheiron insulare.
339
are common in the Bering Sea (Nemoto, 1962a). Thysanoessa raschii
and T . inermis penetrate north of the Bering Straits into the Arctic and
the southern limits of their distributions are immediately south of the
Aleutian Islands Chain. The northern limits of the distributions of the
other three species are north of the Aleutians but they are not common
there although they do occur in the southern half of the Bering Sea.
The horizontal and vertical distributions of the species are shown
diagrammatically in Fig. 126 which represents a section extending
southwards from the Bering Straits. ThysanoZssa inermis, T . raschii
and T . longipes are common in the Sea of Okhotsk while Euphausia
pacijica is very rare ; no other euphausiids live in this subarctic area.
Pacijlc (4O"N-4O0S)
Fifty-nine species are resident in this region but some of the subarctic
and subantarctic species are found south of 40"N and north of 40"s
respectively and so, as in the descriptions of the distributions of the
Atlantic species, these latitudinal limits are only approximate guides to
changing hydrographic regimes and changing euphausiid communities.
Transition zones between subarctic (and subantarctic) and central
Thysanopoda acutifrons; Euphuusia pacijica, E . gibboides;
waters
Thysanoessa gregaria; Nematoscelis dificilis, N . megalops.
Central waters of North and South Pacific
Thysanopoda aequalislT. subaequalis, T . obtusifrons; Euphausia
mutica, E. brevis, E . recurva, E . gibba, E . hemigibba; Nematoscelis
atlantica; Stytocheiron afine " Central Form ", S . suhmii.
Equatorial waters
Thysanopoda tricuspidata; Euphuusia diomedeae, E . tenera, E.
paragibba; Nematoscelis gracilis; Stylocheiron a$ine " W. Equat.
Form ", S. microphthalma.
Central and equatorial waters
Bentheuphausia amblyops; Thysanopoda monacuntha, T . orientalis, T . pectinata; Nematoscelis tenella, N . microps; Nematobrachion
Jlexipes, N . boopis; Xtylocheiron carinatum, 8. elongatum, S. longicorne, X . abbreviatum, S. maximum.
Localized distribution
Nyctiphanes australis, N . simplex; Pseudeuphausia latifrons,
P. sinica; Euphausia eximia, E . nana, E . similis, E. mucronata,
E . sibogae, E. distinguenda, E . lamelligera, E. fallax, E. pseudogibba;
Thysanoessa spinifera; Nematoscelis lobata; Stylocheiron insulare.