3.21 Aetideus arcuatus Vervoort 1949
Snelliaetideus arcuatus Vervoort, 1949: p. 4,
fig. I-Park, 1978: p. 108, figs. 4, 5.
Aetideus arcuatus Roe, 1975: p. 304, fig.
5a-m.
Body length -
females: 1.76-1.96mm (18 specimens)
male:
1.55 (1 specimen)
Female. Body slender. Cephalothorax 2.7
times longer than wide. Head terminates
ventrally in pronounced rostrum with two
strong pointed rami. Margins of last thoracic
somite rounded. Proportional lengths of
cephalothorax and abdomen 77: 23; proportional lengths of abdominal somites and
furca 36: 15 : 12 : 14 : 23 = 100. Genital somite
swollen in dorsal view with large commashaped seminal receptacle in side view.
Genital aperture ovoid in ventral view.
Caudal rami more than 2 times longer than
wide. P4 bears a few small spines and hairs
at base of seta on inner margin of B1. P5
absent.
Male. Body shape similar to female with
same proportions between cephalothorax
and abdomen. Forehead without rostrum.
Posterior corners of cephalothorax rounded.
Abdomen
4-segmented.
Proportional
lengths of abdominal somites and furca
23: 18: 19: 21: 19 = 100. First abdominal
somite asymmetrical with small protuberance
on left side, in dorsal view. P4 Bl lacks
internal spines. P5 present only on left side,
uniramous, 5-jointed; last joint very short,
ending in a cluster of 5 spines and 1 lateral
spine surrounded by a row of small teeth;
inner margin adorned by setae.
Family Aetideidae
Remarks
Vervoort (1949) described Snelliaetideus
arcuatus as a new genus erected to accommodate this species. Bradford (1971a)
noted that the only difference between
Snelliaetideus Vervoort, 1949 and Aetideus
Brady, 1883 females was the absence of
postero-Iateral thoracic points. Roe (1975),
after discovering the male, concluded that
Snelliaetideus was a junior synonym for
Aetideus, a conclusion which is now generally
accepted (Razouls 1993). Our female
specimens, though larger in size, are similar
in morphology to those originally described
by Vervoort. The males concord with the
description given by Roe (1975) except for
the last joint of the P5, which bears a lateral
spine and setae not reported by Roe.
Distribution
The species was recorded for the first time in
the Indo-Pacific Ocean during the Snellius
expedition in the Malay Archipelago
(Vervoort 1949). Since then, it has also
been recorded in the Caribbean Sea (Park
1970), the NE Atlantic (Roe 1975), and the
Antarctic Convergence in the Pacific Ocean
(Park 1978). Its depth of occurrence has been
reported in one haul from 610-790 m (Roe
1975), whereas Park (1978) collected the
species at two stations from 0-1230 m.
To the best of our knowledge, this species
has never been recorded in Chilean and
Argentine waters. In the present study, A.
arcuatus was present from 250-500m at only
three stations in the Pacific area of the Straits
of Magellan.
Snelliaetideus arcuatus Vervoort, 1949: p. 4,
fig. I-Park, 1978: p. 108, figs. 4, 5.
Aetideus arcuatus Roe, 1975: p. 304, fig.
5a-m.
Body length -
females: 1.76-1.96mm (18 specimens)
male:
1.55 (1 specimen)
Female. Body slender. Cephalothorax 2.7
times longer than wide. Head terminates
ventrally in pronounced rostrum with two
strong pointed rami. Margins of last thoracic
somite rounded. Proportional lengths of
cephalothorax and abdomen 77: 23; proportional lengths of abdominal somites and
furca 36: 15 : 12 : 14 : 23 = 100. Genital somite
swollen in dorsal view with large commashaped seminal receptacle in side view.
Genital aperture ovoid in ventral view.
Caudal rami more than 2 times longer than
wide. P4 bears a few small spines and hairs
at base of seta on inner margin of B1. P5
absent.
Male. Body shape similar to female with
same proportions between cephalothorax
and abdomen. Forehead without rostrum.
Posterior corners of cephalothorax rounded.
Abdomen
4-segmented.
Proportional
lengths of abdominal somites and furca
23: 18: 19: 21: 19 = 100. First abdominal
somite asymmetrical with small protuberance
on left side, in dorsal view. P4 Bl lacks
internal spines. P5 present only on left side,
uniramous, 5-jointed; last joint very short,
ending in a cluster of 5 spines and 1 lateral
spine surrounded by a row of small teeth;
inner margin adorned by setae.
Family Aetideidae
Remarks
Vervoort (1949) described Snelliaetideus
arcuatus as a new genus erected to accommodate this species. Bradford (1971a)
noted that the only difference between
Snelliaetideus Vervoort, 1949 and Aetideus
Brady, 1883 females was the absence of
postero-Iateral thoracic points. Roe (1975),
after discovering the male, concluded that
Snelliaetideus was a junior synonym for
Aetideus, a conclusion which is now generally
accepted (Razouls 1993). Our female
specimens, though larger in size, are similar
in morphology to those originally described
by Vervoort. The males concord with the
description given by Roe (1975) except for
the last joint of the P5, which bears a lateral
spine and setae not reported by Roe.
Distribution
The species was recorded for the first time in
the Indo-Pacific Ocean during the Snellius
expedition in the Malay Archipelago
(Vervoort 1949). Since then, it has also
been recorded in the Caribbean Sea (Park
1970), the NE Atlantic (Roe 1975), and the
Antarctic Convergence in the Pacific Ocean
(Park 1978). Its depth of occurrence has been
reported in one haul from 610-790 m (Roe
1975), whereas Park (1978) collected the
species at two stations from 0-1230 m.
To the best of our knowledge, this species
has never been recorded in Chilean and
Argentine waters. In the present study, A.
arcuatus was present from 250-500m at only
three stations in the Pacific area of the Straits
of Magellan.