3.6 Pleuromamma robust a Dahl 1893
Pleuromma robustum Dahl, 1893: p. 104
Pleuromamma robusta Sars, 1903: p. 115,
pIs. ~8, 79 - Steuer, 1933: p. 11, figs. 44,45Ramuez, 1969: p. 73, figs. 95, 96.
Pleuromamma robusta f. antarctica Steuer
1931: p. 7, fig. 2; 1933: p. 11, figs. 56, 57 ~
Vervoort, 1951: p. 123, figs. 68, 69.
Body length -
females: 3.45-3.82mm (5 specimens)
males: 3.14-3.27mm (2 specimens)
Female. Body robust. Cephalothorax 2.5
times longer than wide. Proportional lengths
of cephalothorax and abdomen 68: 32.
Frontal part of head with elongated protrusion ending in rostrum composed of two
filiform processes. Pigmented spot on right
side of cephalothorax. Postero-Iateral
comers of thorax rounded. Abdomen symmetrical. Proportional length of abdominal
somites and furca 41:24:17:18 = 100.
Genital somite symmetrical in dorsal view
with a pronounced ventral swelling in laterai
view. Anal somite produced into distinct
tooth-like comer on each side with three
pores at tip; dorsal distal margin bordered
with a row of denticles and concave area
ornated with short setae. Caudal rami slightly
asymmetrical, left one slightly longer; inner
edge of both rami hairy; dorsal surface of left
ramus with row of long setules along midline.
P5 with 3 free symmetrical joints. First joint
with hairy spine at extreme outer comer.
Second joint with long hairs along inner
border and few hairs along outer edge; outer
edge bears one short naked spine. Terminal
joint with long hairs along both borders. This
joint ends with one long and two much
shorter spines covered with thorns. Between
shorter spines are two short tubules. These
tu~ules appear as small spines at the light
mIcroscope. They are not generally reported
in figures from other authors; only Vervoort's
(1951) drawings of the P5 of P. robusta f.
antarctica are exactly like ours.
Pleuromamma robusta
57
Male. Same shape as female. Basal segment
of Al armed with flattened spatulate aesthetascs. Left Al geniculated. Cephalothorax
2.6 times longer than wide. Proportional
lengths of cephalothorax and abdomen 67: 33.
Pigmented spot on right side of body in the
two specimens we collected. Abdomen
symmetrical and slender; proportional
lengths of abdominal so mites and furca
15: 18: 16: 19: 16 = 100. Third abdominal
somite with a clutch of long hairs on posterior
margin of left side. Anal somite and caudal
rami with same ornamentation as in female.
P5 asymmetrical; left ramus longer than right
with terminal joint narrow and oblong;
te!minal join~ of right ramus considerably
WIdened, lammate and securiform. According to Wilson (1932), the reversed rami of the
~5 with ~espect to other species of the genus
IS a major character of the male of this
species.
Remarks
This species was briefly mentioned by Dahl
(1893) as occurring from 100 to 1500m in the
Atlantic Ocean, but the author gives no
d~t~led description or figures. Steuer (1931)
dIVIded Pleuromamma robusta into two
forms: f. typica [= P. robusta robusta (Dahl
1893)] and f. antarctica [= P. robusta antarctica (Steuer 1931)]. This latter form differs
from the typical one mainly by the scantiness
of the hairs covering the abdominal somites
and furca, both in females and males. The Al
in females is ornated with strong hooks on
the basal joints in the f. typica; in the f.
antarctica, the proximal joints of Al have no
spines or teeth, but the various setae have a
prominent base. In the f. antarctica male no
spinules, tubes or hairs are found along the
edge of the anal operculum. Our specimens
show intermediate characters: the females
lack hook-like teeth on the Al and the P5 is
like the drawings of Vervoort (1951) for P.
robusta f. antarctica; both sexes have an
ornamentation on the anal operculum that
should be lacking in the f. antarctica. Furthermore, they are slightly smaller than
Pleuromma robustum Dahl, 1893: p. 104
Pleuromamma robusta Sars, 1903: p. 115,
pIs. ~8, 79 - Steuer, 1933: p. 11, figs. 44,45Ramuez, 1969: p. 73, figs. 95, 96.
Pleuromamma robusta f. antarctica Steuer
1931: p. 7, fig. 2; 1933: p. 11, figs. 56, 57 ~
Vervoort, 1951: p. 123, figs. 68, 69.
Body length -
females: 3.45-3.82mm (5 specimens)
males: 3.14-3.27mm (2 specimens)
Female. Body robust. Cephalothorax 2.5
times longer than wide. Proportional lengths
of cephalothorax and abdomen 68: 32.
Frontal part of head with elongated protrusion ending in rostrum composed of two
filiform processes. Pigmented spot on right
side of cephalothorax. Postero-Iateral
comers of thorax rounded. Abdomen symmetrical. Proportional length of abdominal
somites and furca 41:24:17:18 = 100.
Genital somite symmetrical in dorsal view
with a pronounced ventral swelling in laterai
view. Anal somite produced into distinct
tooth-like comer on each side with three
pores at tip; dorsal distal margin bordered
with a row of denticles and concave area
ornated with short setae. Caudal rami slightly
asymmetrical, left one slightly longer; inner
edge of both rami hairy; dorsal surface of left
ramus with row of long setules along midline.
P5 with 3 free symmetrical joints. First joint
with hairy spine at extreme outer comer.
Second joint with long hairs along inner
border and few hairs along outer edge; outer
edge bears one short naked spine. Terminal
joint with long hairs along both borders. This
joint ends with one long and two much
shorter spines covered with thorns. Between
shorter spines are two short tubules. These
tu~ules appear as small spines at the light
mIcroscope. They are not generally reported
in figures from other authors; only Vervoort's
(1951) drawings of the P5 of P. robusta f.
antarctica are exactly like ours.
Pleuromamma robusta
57
Male. Same shape as female. Basal segment
of Al armed with flattened spatulate aesthetascs. Left Al geniculated. Cephalothorax
2.6 times longer than wide. Proportional
lengths of cephalothorax and abdomen 67: 33.
Pigmented spot on right side of body in the
two specimens we collected. Abdomen
symmetrical and slender; proportional
lengths of abdominal so mites and furca
15: 18: 16: 19: 16 = 100. Third abdominal
somite with a clutch of long hairs on posterior
margin of left side. Anal somite and caudal
rami with same ornamentation as in female.
P5 asymmetrical; left ramus longer than right
with terminal joint narrow and oblong;
te!minal join~ of right ramus considerably
WIdened, lammate and securiform. According to Wilson (1932), the reversed rami of the
~5 with ~espect to other species of the genus
IS a major character of the male of this
species.
Remarks
This species was briefly mentioned by Dahl
(1893) as occurring from 100 to 1500m in the
Atlantic Ocean, but the author gives no
d~t~led description or figures. Steuer (1931)
dIVIded Pleuromamma robusta into two
forms: f. typica [= P. robusta robusta (Dahl
1893)] and f. antarctica [= P. robusta antarctica (Steuer 1931)]. This latter form differs
from the typical one mainly by the scantiness
of the hairs covering the abdominal somites
and furca, both in females and males. The Al
in females is ornated with strong hooks on
the basal joints in the f. typica; in the f.
antarctica, the proximal joints of Al have no
spines or teeth, but the various setae have a
prominent base. In the f. antarctica male no
spinules, tubes or hairs are found along the
edge of the anal operculum. Our specimens
show intermediate characters: the females
lack hook-like teeth on the Al and the P5 is
like the drawings of Vervoort (1951) for P.
robusta f. antarctica; both sexes have an
ornamentation on the anal operculum that
should be lacking in the f. antarctica. Furthermore, they are slightly smaller than