3.15 Neocalanus tonsus Brady 1883
Calanus tonsus Brady, 1883: p. 34, pI. 4 figs.
8 9- Wolfenden, 1908: p. 11, pl.,..l figs. 7, 8Farran, 1929: p. 216, fig. 2 - Brodskii, 1948:
p. 32, pI. 3 figs. 1-7, pI. 4 figs. 1,2; 1950: p.
92, fig. 22 (c. tonsus f. plumchrus and f.
typica) - Tanaka, 1956a: p. 49, figs. 1-4 -
Vervoort, 1957: p. 27, figs. 3-6 - Jillett,
1968: p. 27, fig. 3.
Neocalanus tonsus Bradford, 1988: p. 79.
Body length -
female: 3.92mm (1 specimen)
Female. Cephalothorax elongated and tapering towards the head with poorly defined
protuberance. Cephalothorax of our ~nly
specimen 2.8 times longer th~n wI~e.
Posterior corners of last thoracIc somIte
produced backward into short round processes. Proportional lengths of cephalothorax
and abdomen 79: 21; proportional lengths of
abdominal somites and furca 42 : 22 : 11 : 11 : 14
= 100. P5 Bl with smooth inner margins
without teeth; B2 with 4 spines on distal
inner surface.
Remarks
In our samples, we recorded only copepodite
specimens and one adult female. Unfortunately, this latter was heavily da~aged,
with a P5 having only Bl. AccordIng to
Brodskii (1950), there are two forms of this
species: f. typica and f. plumchrus, the latter
being synonymous with Calanus plumchrus
Marukawa. The only difference between
these forms is the presence of elongated, very
Neocalanus tonsus
105
hairy caudal bristles in the CV of f. plumchrus.
Brodskii (1950) stated that possibly f.
plumchrus represents a seasonal form.
Distribution
N. tons us is an abundant oceanic, autiboreal
copepod distributed mainly in the subAntarctic, from New Zealand across the
Southern Pacific, but not entering the true
Antarctic region (Jillett 1968). It is abundant
over the edges of the continental shelf and
slope, somewhat less plentiful over oceanic
depths, but avoids neritic conditions inshore.
This was the dominant species found by
Marin and Antezana (1985)- in Chilean
fjords, where it was present only .. as
copepodite stages (mainly CV) compnsIn.g
32-89% of the copepod stock. N. tonsus IS
also reported for the Atlantic, north of the
Patagonian region, in external slope waters
subjected to sub-Antarctic currents (Ramirez
1971). The depth of occurr~nce of this
species varies seasonally; Jdlett (1968)
reports it as abundant in the upper 150 m
layer from midspring to midsummer (October
to January) but it was virtually absent from
surface waters from late summer (February)
until spring (September), when it again
became abundant. Ohman (1987) maintains
that reproductive copepods of this speci~s
occur in mesopelagic depths (500-1000m) In
austral winter and epipelagic depths (0150m) in spring. In the present study, N.
tonsus was found only from 150-200m at a
Pacific station in the Straits of Magellan. It
was also sporadically present throughout the
water column at two other stations in the
Central area with maximum abundances
from 300-400 m.
Calanus tonsus Brady, 1883: p. 34, pI. 4 figs.
8 9- Wolfenden, 1908: p. 11, pl.,..l figs. 7, 8Farran, 1929: p. 216, fig. 2 - Brodskii, 1948:
p. 32, pI. 3 figs. 1-7, pI. 4 figs. 1,2; 1950: p.
92, fig. 22 (c. tonsus f. plumchrus and f.
typica) - Tanaka, 1956a: p. 49, figs. 1-4 -
Vervoort, 1957: p. 27, figs. 3-6 - Jillett,
1968: p. 27, fig. 3.
Neocalanus tonsus Bradford, 1988: p. 79.
Body length -
female: 3.92mm (1 specimen)
Female. Cephalothorax elongated and tapering towards the head with poorly defined
protuberance. Cephalothorax of our ~nly
specimen 2.8 times longer th~n wI~e.
Posterior corners of last thoracIc somIte
produced backward into short round processes. Proportional lengths of cephalothorax
and abdomen 79: 21; proportional lengths of
abdominal somites and furca 42 : 22 : 11 : 11 : 14
= 100. P5 Bl with smooth inner margins
without teeth; B2 with 4 spines on distal
inner surface.
Remarks
In our samples, we recorded only copepodite
specimens and one adult female. Unfortunately, this latter was heavily da~aged,
with a P5 having only Bl. AccordIng to
Brodskii (1950), there are two forms of this
species: f. typica and f. plumchrus, the latter
being synonymous with Calanus plumchrus
Marukawa. The only difference between
these forms is the presence of elongated, very
Neocalanus tonsus
105
hairy caudal bristles in the CV of f. plumchrus.
Brodskii (1950) stated that possibly f.
plumchrus represents a seasonal form.
Distribution
N. tons us is an abundant oceanic, autiboreal
copepod distributed mainly in the subAntarctic, from New Zealand across the
Southern Pacific, but not entering the true
Antarctic region (Jillett 1968). It is abundant
over the edges of the continental shelf and
slope, somewhat less plentiful over oceanic
depths, but avoids neritic conditions inshore.
This was the dominant species found by
Marin and Antezana (1985)- in Chilean
fjords, where it was present only .. as
copepodite stages (mainly CV) compnsIn.g
32-89% of the copepod stock. N. tonsus IS
also reported for the Atlantic, north of the
Patagonian region, in external slope waters
subjected to sub-Antarctic currents (Ramirez
1971). The depth of occurr~nce of this
species varies seasonally; Jdlett (1968)
reports it as abundant in the upper 150 m
layer from midspring to midsummer (October
to January) but it was virtually absent from
surface waters from late summer (February)
until spring (September), when it again
became abundant. Ohman (1987) maintains
that reproductive copepods of this speci~s
occur in mesopelagic depths (500-1000m) In
austral winter and epipelagic depths (0150m) in spring. In the present study, N.
tonsus was found only from 150-200m at a
Pacific station in the Straits of Magellan. It
was also sporadically present throughout the
water column at two other stations in the
Central area with maximum abundances
from 300-400 m.