182
Systematic Account
3.32 Paraeuchaeta biloba
Farran 1929
Pareuchaeta bi/aba Farran, 1929: p. 242, fig.
11 - Bradford et aI., 1983: p. 29, figs. 3, 4,
81.
Euchaeta bi/aba Vervoort, 1957: p. 79, figs.
60-68 - Park, 1978: p. 217, figs. 74-76.
Body length -
females: 5.43-5.64mm (3 specimens)
male:
5.00mm (1 specimen)
Female. Body slender in dorsal view.
Cephalothorax 2.5 times longer than wide.
Proportional lengths of cephalothorax and
abdomen 62: 38. In dorsal view, head slightly
protruding into frontal organ bearing two
sensilla. Rostrum moderately developed,
slightly protruding forwards. Postero-Iateral
corners of last thoracic somite broadly
rounded both in dorsal and lateral views.
Patches of hairs of different length and width
on apex of each corner; tuft of long hairs on
postero-Iateral margins. Abdomen 4segmented;
proportional
lengths
of
abdominal somites and furca 38 : 24 : 24 : 2 : 12
= 100. Genital somite long and slender,
symmetrical in dorsal view. Genital prominence bilobed in lateral view; hairy distal
part of ventral surface. Dorsal margins of all
abdominal so mites with small spinules. Third
somite with sparse, long hairs on dorsal
surface. Anal somite very short. Caudal rami
about twice as long as wide, with long hairs
on both inner and outer margins. Inner apical
caudal setae originating from short cylindrical
processes, geniculated and much longer than
terminal setae.
Male. Body more slender than female.
Cephalothorax 3 times longer than wide.
Proportional lengths of cephalothorax and
abdomen 90: 41. Head triangular in dorsal
view with prominent frontal organ bearing
two sensilla. Rostrum slender and slightly
longer than in female. Postero-Iateral borders
of last thoracic somite rounded, slightly prolonged in dorsal view, with tooth-like processes on dorsal margins, tufts of long hairs
on ventral and lateral sides, and patch of
small spinules on dorso-Iateral margins.
Abdomen 5-segmented; proportional lengths
of abdominal somites and furca 22: 29 : 24 :
17:2:6 = 100. Genital somite asymmetrical,
more produced on left side in dorsal view; in
lateral view, bearing a distinct tubercle on
ventral side, slightly overlapping second
abdominal somite. Successive somites (2nd4th) armed with triangular teeth along dorsal
distal margins, particularly developed on
fourth somite. Caudal rami more or less as
long as wide, with long hairs on inner borders.
P5 biramous. Re2 of right leg styliform
almost as long as first; endo'pod 1-jointed as
long as Re1. Left endopod vestigial. Re2 of
left leg with serrated lamella prolonged distally into strong spiniform process; basal
portion of lamella hollow, each edge bearing
large tooth together with number of small
teeth. Re2 also with grooved digitiform process. Re3 hollow, ending in acute point and
ornated with tuft of very strong, long bristles.
Distribution
P. bi/aba was originally recorded by Farran
(1929) in surface waters north of the Atlantic
Convergence and at depths between 0 and
400 m at the entrance of the Ross Sea. Hardy
and Gunther (1935) reported it at intermediate depths in the South Georgia area.
According to Ward and Wood (1988), P.
bi/aba was one of the dominant euchaetid
species around South Georgia with a vertical
distribution centered in epi-mesopelagic
(250-500m) and mesopelagic (500-1000m)
waters, both in summer and winter. Vervoort
(1957) found this species in the Banzare
collections between 45°1O'S and 650ZTS in
the Indian Ocean and also south of Tasmania.
Park (1978) reported P. bilaba as one of the
most common euchaetid species in the Pacific
(between 39°24'S and 68°40'S) and Atlantic
(between 34°43'S and 57°04'S) Oceans.
Bradford et al. (1983) recorded this species in
the SW Pacific off New Zealand down to
1000 m. P. bilaba inhabits surface and
intermediate waters of Antarctic and sub-
Systematic Account
3.32 Paraeuchaeta biloba
Farran 1929
Pareuchaeta bi/aba Farran, 1929: p. 242, fig.
11 - Bradford et aI., 1983: p. 29, figs. 3, 4,
81.
Euchaeta bi/aba Vervoort, 1957: p. 79, figs.
60-68 - Park, 1978: p. 217, figs. 74-76.
Body length -
females: 5.43-5.64mm (3 specimens)
male:
5.00mm (1 specimen)
Female. Body slender in dorsal view.
Cephalothorax 2.5 times longer than wide.
Proportional lengths of cephalothorax and
abdomen 62: 38. In dorsal view, head slightly
protruding into frontal organ bearing two
sensilla. Rostrum moderately developed,
slightly protruding forwards. Postero-Iateral
corners of last thoracic somite broadly
rounded both in dorsal and lateral views.
Patches of hairs of different length and width
on apex of each corner; tuft of long hairs on
postero-Iateral margins. Abdomen 4segmented;
proportional
lengths
of
abdominal somites and furca 38 : 24 : 24 : 2 : 12
= 100. Genital somite long and slender,
symmetrical in dorsal view. Genital prominence bilobed in lateral view; hairy distal
part of ventral surface. Dorsal margins of all
abdominal so mites with small spinules. Third
somite with sparse, long hairs on dorsal
surface. Anal somite very short. Caudal rami
about twice as long as wide, with long hairs
on both inner and outer margins. Inner apical
caudal setae originating from short cylindrical
processes, geniculated and much longer than
terminal setae.
Male. Body more slender than female.
Cephalothorax 3 times longer than wide.
Proportional lengths of cephalothorax and
abdomen 90: 41. Head triangular in dorsal
view with prominent frontal organ bearing
two sensilla. Rostrum slender and slightly
longer than in female. Postero-Iateral borders
of last thoracic somite rounded, slightly prolonged in dorsal view, with tooth-like processes on dorsal margins, tufts of long hairs
on ventral and lateral sides, and patch of
small spinules on dorso-Iateral margins.
Abdomen 5-segmented; proportional lengths
of abdominal somites and furca 22: 29 : 24 :
17:2:6 = 100. Genital somite asymmetrical,
more produced on left side in dorsal view; in
lateral view, bearing a distinct tubercle on
ventral side, slightly overlapping second
abdominal somite. Successive somites (2nd4th) armed with triangular teeth along dorsal
distal margins, particularly developed on
fourth somite. Caudal rami more or less as
long as wide, with long hairs on inner borders.
P5 biramous. Re2 of right leg styliform
almost as long as first; endo'pod 1-jointed as
long as Re1. Left endopod vestigial. Re2 of
left leg with serrated lamella prolonged distally into strong spiniform process; basal
portion of lamella hollow, each edge bearing
large tooth together with number of small
teeth. Re2 also with grooved digitiform process. Re3 hollow, ending in acute point and
ornated with tuft of very strong, long bristles.
Distribution
P. bi/aba was originally recorded by Farran
(1929) in surface waters north of the Atlantic
Convergence and at depths between 0 and
400 m at the entrance of the Ross Sea. Hardy
and Gunther (1935) reported it at intermediate depths in the South Georgia area.
According to Ward and Wood (1988), P.
bi/aba was one of the dominant euchaetid
species around South Georgia with a vertical
distribution centered in epi-mesopelagic
(250-500m) and mesopelagic (500-1000m)
waters, both in summer and winter. Vervoort
(1957) found this species in the Banzare
collections between 45°1O'S and 650ZTS in
the Indian Ocean and also south of Tasmania.
Park (1978) reported P. bilaba as one of the
most common euchaetid species in the Pacific
(between 39°24'S and 68°40'S) and Atlantic
(between 34°43'S and 57°04'S) Oceans.
Bradford et al. (1983) recorded this species in
the SW Pacific off New Zealand down to
1000 m. P. bilaba inhabits surface and
intermediate waters of Antarctic and sub-