88 Chapter 4 Euphausiids
tezana 1976). In fact, Mayer (1969), based on individuals collected off the 5outh American continent, proposed that both species be included as
one, with a wide range of individual variation of
the petasma and of the first segment of the antennule. Mayer's illustrations, however, showed
the characteristics allowing for the identification
ofboth species. Furthermore, the author's figs. 4,
5, 7 and 8 correspond to juveniles. Mayer's questioning the validity of both species, particularly
the frequent absence of a spine on the 3rd abdominal segment of E. vallentini, and variability
and overlapping of other diagnostic features, allows us to point out the following as additional
distinguishing features: size and shape of the
dorsal keel of the 3rd antennular segment, denticles on the inner border of the subterminal
spines, and distribution of setae on the setiferous labe of the petasma. It should be remarked
that specimens collected in the northern extension of the Chilean fjords and in the Humboldt
Current up to 38°5 (Antezana 1976, 1978, 1981)
fit the above description of the species; none carry a spine on the 3rd abdominal segment.
Distribution
E. vallentini is endemic to the southern hemisphere with a typically sub-Antarctic circumpolar distribution extending between the 5ubtropical Convergence and the Antarctic Convergence (John 1936). It has been exceptionally collected also beyond these boundaries (Zimmer
1915; Lomakina 1964 ). Off 5outh America, E.
vallentini is found in Atlantic and Pacific waters,
including southern Chilean fjords.
In Atlantic waters near South America, only
spineless individuals have been found (Antezana
and Brinton 1981). The geographic distribution
of E. vallentini in the Eastern 5outh Pacific is divided into 2 areas: an oceanic West Wind Drift
area south of 48°5, extending to the Antarctic
Convergence, and a coastal area between 384205 in the Humboldt Current. E. vallentini is
concentrated in the area between 53-57°5 reaching coastal areas as well, where it is the most
abundant sub-Antarctic species (Antezana 1978,
1981). Within the fjords of Chile (including a few
stations in the 5traits of Magellan), E. vallentini
was the most frequently encountered and a bundant euphausiid accounting for the greatest proportion of the net-zooplankton biomass (Antezana 1976). Guglielmo et al. {1991) and Antezana
et al. ( 1992) also identified it as the dominant euphausiid species within the 5traits.
In the present study, both spiny and spineless
individuals were observed. Only juveniles (calyptopis and furcilia stages) were sampled in the
Pacific area, with totallengths ranging from 57 mm (5ts. 5 and 6) to 8-10 mm (5ts. 9 and 11).
The number of adults and juveniles progressively increased towards the centre of the 5traits,
with maximum densities at 5t. 18. Only a small
number of adult specimens were sampled in the
Atlantic (5t. 26). The species was present at all
depths but maximum numbers were recorded
from 150-200 m at Central and Pacific stations,
where it undergoes ample diel vertical migrations.
tezana 1976). In fact, Mayer (1969), based on individuals collected off the 5outh American continent, proposed that both species be included as
one, with a wide range of individual variation of
the petasma and of the first segment of the antennule. Mayer's illustrations, however, showed
the characteristics allowing for the identification
ofboth species. Furthermore, the author's figs. 4,
5, 7 and 8 correspond to juveniles. Mayer's questioning the validity of both species, particularly
the frequent absence of a spine on the 3rd abdominal segment of E. vallentini, and variability
and overlapping of other diagnostic features, allows us to point out the following as additional
distinguishing features: size and shape of the
dorsal keel of the 3rd antennular segment, denticles on the inner border of the subterminal
spines, and distribution of setae on the setiferous labe of the petasma. It should be remarked
that specimens collected in the northern extension of the Chilean fjords and in the Humboldt
Current up to 38°5 (Antezana 1976, 1978, 1981)
fit the above description of the species; none carry a spine on the 3rd abdominal segment.
Distribution
E. vallentini is endemic to the southern hemisphere with a typically sub-Antarctic circumpolar distribution extending between the 5ubtropical Convergence and the Antarctic Convergence (John 1936). It has been exceptionally collected also beyond these boundaries (Zimmer
1915; Lomakina 1964 ). Off 5outh America, E.
vallentini is found in Atlantic and Pacific waters,
including southern Chilean fjords.
In Atlantic waters near South America, only
spineless individuals have been found (Antezana
and Brinton 1981). The geographic distribution
of E. vallentini in the Eastern 5outh Pacific is divided into 2 areas: an oceanic West Wind Drift
area south of 48°5, extending to the Antarctic
Convergence, and a coastal area between 384205 in the Humboldt Current. E. vallentini is
concentrated in the area between 53-57°5 reaching coastal areas as well, where it is the most
abundant sub-Antarctic species (Antezana 1978,
1981). Within the fjords of Chile (including a few
stations in the 5traits of Magellan), E. vallentini
was the most frequently encountered and a bundant euphausiid accounting for the greatest proportion of the net-zooplankton biomass (Antezana 1976). Guglielmo et al. {1991) and Antezana
et al. ( 1992) also identified it as the dominant euphausiid species within the 5traits.
In the present study, both spiny and spineless
individuals were observed. Only juveniles (calyptopis and furcilia stages) were sampled in the
Pacific area, with totallengths ranging from 57 mm (5ts. 5 and 6) to 8-10 mm (5ts. 9 and 11).
The number of adults and juveniles progressively increased towards the centre of the 5traits,
with maximum densities at 5t. 18. Only a small
number of adult specimens were sampled in the
Atlantic (5t. 26). The species was present at all
depths but maximum numbers were recorded
from 150-200 m at Central and Pacific stations,
where it undergoes ample diel vertical migrations.