6.1 Mikroconchoecia cf. acuticosta
Miiller, 1906
Conchoecia acuticosta Miiller, 1906a: p. 87, pl. 30
figs. 18-21- Angel, 1981: p. 556, fig. 194/15.
Microconchoecia acuticosta Poulsen, 1973: p. 67.
Conchoecia (Microconchoecia) acuticosta Deevey, 1978: p. 69, 70, fig. 14- Deevey, 1982: p. 156,
fig. 27.
Mikroconchoecia aff. acuticosta Martens, 1979:
p. 349.
Carapace length -
females: 0.98-1.26 mm
males: 1.10-1.30 mm
Female. Carapace rectangular, squat and short;
the height:length ratio is about 0.65; rostrum
slightly curved; incisure broad and moderately
deep; dorsal margin relatively straight, apart
from weakly developed shoulders; posterior
margin convex, posterodorsally each valve ends
in a barely discernible blunted tip; ventral margin likewise convex and smoothly curved. Shell
sculpture (ornament) distinct, consisting of very
thin parallel riblets posteriorly and ventrally, becoming reticulate toward the centre of each valve
and anteriorly; the intersection of this meshwork
with the anteroventral margin produces a denticulate effect. Both asymmetric glands in their
usual places, i.e. postero-dorsal in the left valve
and near postero-ventral in the right valve; the
right gland is large and prominent ( this is a good
differentiating character between acuticosta and
the type species M. curta). Cap of the frontal organ short and smooth, united with but somewhat thicker than the stern. All limbs relatively
short. Al indistinctly segmented in front; of the 5
end bristles, the 'e' bristle is about as long as the
segments combined, 3 of the sensory 'pipe' brisSubphylum CRUSTACEA
Class OSTRACODA
Order HALOCYPRIDA
Planktonic Halocyprida
Family Halocyprididae
tles are shorter and deeply bifurcate, the 4th is
simple but about the same length. Furca with 8
claws separated from the lamella and reducing in
size rearwards; there is no unpaired posterior
bristle.
Male. Carapace similar to that of female. Cap of
the frontal organ separated from the stern by a
distinct joint, broadly rounded in front on our
specimens and smooth. Al with 5 end bristles;
the 'e' bristle ornamented with a single series of
12 spinules; of the 4 sensory 'pipe' bristles, 2 are
slender and nearly as long as the chief bristle, a
3rd is shorter and deeply bifurcate, and the last is
simple and short. The clasping joints of the A2
are dimorphic; the right one is relatively slender
and strongly recurved with a retrousse tip (unlike M. curta), the left one is short and almost
straight. Penis rather short and stout, with
somewhat sinuous margins and a broadly
rounded front; a few transverse muscle bands;
seminal tube simple.
Remarks
Only a few specimens were found, in samples
from five Magellan Stations (7, 16, 18, 20, 21). We
follow Martens (1979) in assigning this species
with some hesitation. Our adults are smaller
than the size range given by Angel ( 1981). On the
other hand, Martens (1979), Angel (1981) and
Deevey (1983) all recorded M. curta (Lubbock
1860)- our first determination for this form- as
only occurring north of 47°S; while Martens
(1979) identified M. acuticosta as the more austral representative of this rather similar pair of
species. Martens (1979) also noted that the carapace sculpture is very variable, even in specimens from the same haul, and sometimes is almost invisible.
Miiller, 1906
Conchoecia acuticosta Miiller, 1906a: p. 87, pl. 30
figs. 18-21- Angel, 1981: p. 556, fig. 194/15.
Microconchoecia acuticosta Poulsen, 1973: p. 67.
Conchoecia (Microconchoecia) acuticosta Deevey, 1978: p. 69, 70, fig. 14- Deevey, 1982: p. 156,
fig. 27.
Mikroconchoecia aff. acuticosta Martens, 1979:
p. 349.
Carapace length -
females: 0.98-1.26 mm
males: 1.10-1.30 mm
Female. Carapace rectangular, squat and short;
the height:length ratio is about 0.65; rostrum
slightly curved; incisure broad and moderately
deep; dorsal margin relatively straight, apart
from weakly developed shoulders; posterior
margin convex, posterodorsally each valve ends
in a barely discernible blunted tip; ventral margin likewise convex and smoothly curved. Shell
sculpture (ornament) distinct, consisting of very
thin parallel riblets posteriorly and ventrally, becoming reticulate toward the centre of each valve
and anteriorly; the intersection of this meshwork
with the anteroventral margin produces a denticulate effect. Both asymmetric glands in their
usual places, i.e. postero-dorsal in the left valve
and near postero-ventral in the right valve; the
right gland is large and prominent ( this is a good
differentiating character between acuticosta and
the type species M. curta). Cap of the frontal organ short and smooth, united with but somewhat thicker than the stern. All limbs relatively
short. Al indistinctly segmented in front; of the 5
end bristles, the 'e' bristle is about as long as the
segments combined, 3 of the sensory 'pipe' brisSubphylum CRUSTACEA
Class OSTRACODA
Order HALOCYPRIDA
Planktonic Halocyprida
Family Halocyprididae
tles are shorter and deeply bifurcate, the 4th is
simple but about the same length. Furca with 8
claws separated from the lamella and reducing in
size rearwards; there is no unpaired posterior
bristle.
Male. Carapace similar to that of female. Cap of
the frontal organ separated from the stern by a
distinct joint, broadly rounded in front on our
specimens and smooth. Al with 5 end bristles;
the 'e' bristle ornamented with a single series of
12 spinules; of the 4 sensory 'pipe' bristles, 2 are
slender and nearly as long as the chief bristle, a
3rd is shorter and deeply bifurcate, and the last is
simple and short. The clasping joints of the A2
are dimorphic; the right one is relatively slender
and strongly recurved with a retrousse tip (unlike M. curta), the left one is short and almost
straight. Penis rather short and stout, with
somewhat sinuous margins and a broadly
rounded front; a few transverse muscle bands;
seminal tube simple.
Remarks
Only a few specimens were found, in samples
from five Magellan Stations (7, 16, 18, 20, 21). We
follow Martens (1979) in assigning this species
with some hesitation. Our adults are smaller
than the size range given by Angel ( 1981). On the
other hand, Martens (1979), Angel (1981) and
Deevey (1983) all recorded M. curta (Lubbock
1860)- our first determination for this form- as
only occurring north of 47°S; while Martens
(1979) identified M. acuticosta as the more austral representative of this rather similar pair of
species. Martens (1979) also noted that the carapace sculpture is very variable, even in specimens from the same haul, and sometimes is almost invisible.