334
THE BIOLOGY OF EUPHAUSIIDS
Central waters and transition zones between subarctic (and subEuphausia krohnii, E . recuma, E . hemigibba; Thysanoessa
antarctic) and central waters
gregaria; Nematoscelis megalops.
Equatorial waters
cana.
Central and equatorial waters
Bentheuphausia amblyops; Thysanopoda monacantha, T . aequalisl
T . subaequalis, T . obtusifrons, T . pectinata; Euphausia mutica,
E. brevis, E . tenera, E . gibboides, E . pseudogibba; Thysanoessa parva;
Nematoscelis tenella, N . micropslN. atlantica; Nematobrachion
Jlexipes, N . boopis; Stylocheiron carinatum, S. afine, S. suhmii,
8. elongatum, S. longicorne, S. abbreviatum, S. maximum.
Localized distribution
Thysanopoda tricuspidata, T . microphthalma; Euphausia ameriNyctiphanes capensis, N . simplex; Euphausia hanseni.
Rare species whose distribution is only approximately known
Thysanopoda cristata, T . orientalis, T . cornuta, T . egregia;
Euphausia eximia; Nematobrachion sexspinosum; Stylocheiron microphthalma, S. insulare, s. robustum.
Euphausia recurva is present off northwest Africa (Boden, 1961a)
but this is the only record of it north of the latitudinal band 20"s to
4073, in which it occurs in the southern Atlantic. Euphausia krohnii
occurs between 20"N and 40"N but is a frequent guest in areas north of
40"N. The other three species found in the central waters have
bi-antitropical distributions, being absent from equatorial regions.
They occur inside the bipolar distributional areas of Thysanopoda
acutifrons; Euphausia hemigibba has its distributional area closest to the
equator while Nematoscelis megalops and the deeper living Thysanoessa
gregaria share the same areas which are further removed from the
equator than those of Euphausia hemigibba. The bipolar species,
Thysanopoda acutifrons, occupies the area north of the northern areas
of distribution of these former three species but shares their southern
regions of occurrence ; its distributional areas in the Atlantic, Pacific,
and Indian Oceans roughly lie between the limits of the 5°C and the
10°C isotherms a t 200 m depth but the temperature limitations of the
distribution of the other species seem to be different in different parts
of the Atlantic and Pacific.
Thysanopoda tricuspidata and T . microphthalma are restricted to
THE BIOLOGY OF EUPHAUSIIDS
Central waters and transition zones between subarctic (and subEuphausia krohnii, E . recuma, E . hemigibba; Thysanoessa
antarctic) and central waters
gregaria; Nematoscelis megalops.
Equatorial waters
cana.
Central and equatorial waters
Bentheuphausia amblyops; Thysanopoda monacantha, T . aequalisl
T . subaequalis, T . obtusifrons, T . pectinata; Euphausia mutica,
E. brevis, E . tenera, E . gibboides, E . pseudogibba; Thysanoessa parva;
Nematoscelis tenella, N . micropslN. atlantica; Nematobrachion
Jlexipes, N . boopis; Stylocheiron carinatum, S. afine, S. suhmii,
8. elongatum, S. longicorne, S. abbreviatum, S. maximum.
Localized distribution
Thysanopoda tricuspidata, T . microphthalma; Euphausia ameriNyctiphanes capensis, N . simplex; Euphausia hanseni.
Rare species whose distribution is only approximately known
Thysanopoda cristata, T . orientalis, T . cornuta, T . egregia;
Euphausia eximia; Nematobrachion sexspinosum; Stylocheiron microphthalma, S. insulare, s. robustum.
Euphausia recurva is present off northwest Africa (Boden, 1961a)
but this is the only record of it north of the latitudinal band 20"s to
4073, in which it occurs in the southern Atlantic. Euphausia krohnii
occurs between 20"N and 40"N but is a frequent guest in areas north of
40"N. The other three species found in the central waters have
bi-antitropical distributions, being absent from equatorial regions.
They occur inside the bipolar distributional areas of Thysanopoda
acutifrons; Euphausia hemigibba has its distributional area closest to the
equator while Nematoscelis megalops and the deeper living Thysanoessa
gregaria share the same areas which are further removed from the
equator than those of Euphausia hemigibba. The bipolar species,
Thysanopoda acutifrons, occupies the area north of the northern areas
of distribution of these former three species but shares their southern
regions of occurrence ; its distributional areas in the Atlantic, Pacific,
and Indian Oceans roughly lie between the limits of the 5°C and the
10°C isotherms a t 200 m depth but the temperature limitations of the
distribution of the other species seem to be different in different parts
of the Atlantic and Pacific.
Thysanopoda tricuspidata and T . microphthalma are restricted to