3.40 Oithona similis Claus 1866
Oithona similis Claus, 1966: p. 14 -
Giesbrecht, 1892: p. 537, pI. 34 figs. 18, 19,
21,36-39, pI. 44 figs. 3, 5, 8-11- Rosendorn,
1917: p. 24, fig. 13a-e - Mori, 1937: p. 112,
pI. 62 figs. 1-12 - Tanaka, 1960a: p. 62, pI.
27 figs. 1-9 - Nishida et aI., 1977: p. 149,
figs. 21a-h, 22a-c - Nishida, 1985: p. 88,
figs. 50, 51.
Oithona helgolandica Claus, 1863: p. 105, pI.
1 fig. 2 - Sars, 1918: p. 8, pI. 3.
Body length -
females: 0.80-0.92mm (39 specimens)
Female. Prosome elongated, ellipsoid in
dorsal view, 2.6 times longer than wide, 1.2
times urosome. Head truncated anteriorly in
dorsal view; in lateral view produced ventrally
into sharply pointed rostrum. Proportional
lengths of urosomites and furca 15: 36: 14:
12: 12: 11 = 100. Anterior 113 of genital
somite swollen laterally. P1-P4 Re with
1,1,2; 1,0,1; 1,0,1; 0,0,1 outer marginal
spines and 0,1,4; 0,1,5; 0,1,5; 0,1,5 inner
marginal setae. Outer marginal spine on P4
Re3 minute.
Remarks
Our specimens agree in general shape, size
range and swimming legs with the typical O.
similis. There seems to be some confusion
about the name of this species, as reported by
Oithona similis
219
Crisafi (1959), Ramirez (1969) and Nishida et
al. (1977), who widely discussed the relationships between O. similis and O. helgolandica.
Nishida et al. (1977) are of the opinion that
the species described as O. helgolandica by
Claus (1863) should be rejected.
Distribution
O. similis is considered a cosmopolitan
species with a very wide geographical distribution. Farran (1929) reported O. similis
common in the Pacific sector of the Antarctic
and frequent in hauls made under the ice. It
has been reported in the Atlantic Sector of
the Antarctic by Vervoort (1951). Its distribution in the Pacific and Indian Oceans is
discussed by Nishida (1985), who reported
this species as very abundant in sub-Arctic,
sub-Antarctic and Antarctic waters. Bradford
(1971b) reported O. similis as abundant in
the Ross Sea (Antarctica) and in the warm
deep waters of the Antarctic. North of the
Antarctic Convergence, it occurs in surface
waters (Vervoort 1957). Ramirez (1969, 1977)
reported O. helgolandica as common in
Argentine waters. Hirakawa (1989) reported
O. similis for southern Chilean fjords.
According to Nishida (1985), it is still
unknown if there are morphologically distinct populations within the wide geographical
range of o. similis. In the present study, it
was one of the most frequently sampled
species. It was recorded at all depths but with
maximum abundances in the upper 50 m.
Oithona similis Claus, 1966: p. 14 -
Giesbrecht, 1892: p. 537, pI. 34 figs. 18, 19,
21,36-39, pI. 44 figs. 3, 5, 8-11- Rosendorn,
1917: p. 24, fig. 13a-e - Mori, 1937: p. 112,
pI. 62 figs. 1-12 - Tanaka, 1960a: p. 62, pI.
27 figs. 1-9 - Nishida et aI., 1977: p. 149,
figs. 21a-h, 22a-c - Nishida, 1985: p. 88,
figs. 50, 51.
Oithona helgolandica Claus, 1863: p. 105, pI.
1 fig. 2 - Sars, 1918: p. 8, pI. 3.
Body length -
females: 0.80-0.92mm (39 specimens)
Female. Prosome elongated, ellipsoid in
dorsal view, 2.6 times longer than wide, 1.2
times urosome. Head truncated anteriorly in
dorsal view; in lateral view produced ventrally
into sharply pointed rostrum. Proportional
lengths of urosomites and furca 15: 36: 14:
12: 12: 11 = 100. Anterior 113 of genital
somite swollen laterally. P1-P4 Re with
1,1,2; 1,0,1; 1,0,1; 0,0,1 outer marginal
spines and 0,1,4; 0,1,5; 0,1,5; 0,1,5 inner
marginal setae. Outer marginal spine on P4
Re3 minute.
Remarks
Our specimens agree in general shape, size
range and swimming legs with the typical O.
similis. There seems to be some confusion
about the name of this species, as reported by
Oithona similis
219
Crisafi (1959), Ramirez (1969) and Nishida et
al. (1977), who widely discussed the relationships between O. similis and O. helgolandica.
Nishida et al. (1977) are of the opinion that
the species described as O. helgolandica by
Claus (1863) should be rejected.
Distribution
O. similis is considered a cosmopolitan
species with a very wide geographical distribution. Farran (1929) reported O. similis
common in the Pacific sector of the Antarctic
and frequent in hauls made under the ice. It
has been reported in the Atlantic Sector of
the Antarctic by Vervoort (1951). Its distribution in the Pacific and Indian Oceans is
discussed by Nishida (1985), who reported
this species as very abundant in sub-Arctic,
sub-Antarctic and Antarctic waters. Bradford
(1971b) reported O. similis as abundant in
the Ross Sea (Antarctica) and in the warm
deep waters of the Antarctic. North of the
Antarctic Convergence, it occurs in surface
waters (Vervoort 1957). Ramirez (1969, 1977)
reported O. helgolandica as common in
Argentine waters. Hirakawa (1989) reported
O. similis for southern Chilean fjords.
According to Nishida (1985), it is still
unknown if there are morphologically distinct populations within the wide geographical
range of o. similis. In the present study, it
was one of the most frequently sampled
species. It was recorded at all depths but with
maximum abundances in the upper 50 m.