3.12 Themisto gaudichaudii Guerin, 1828
Themisto gaudichaudii Guerin, 1828: p. 774
Euthemisto gaudichaudii Bovallius, 1889: p. 299,
figs. 1-5, pl. 13 figs. 44-46.
Parathemisto (Euthemisto) gaudichaudii Hurley,
1955: p. 161, figs. 159-174.
Parathemisto gaudichaudii Sheader and Evans,
1974: p. 915 (key) - Sheader, 1975: p. 887 -
Schneppenheim and Weigmann-Haass, 1986: p.
219, figs. 1, la, p. 222 (key).
Body length -
females: 6.4-13.0 mm (30 specimens)
males: 7.0-13.0 mm (30 specimens)
Female. Body keel-like dorsally with strong dorsai spines about ;::: 1 O mm in length. Article 4 of
Al curved. Flagellum of A2 with one article. Anterior extremity ofP2 merus rounded. P3 and P4
with dilated carpus that together with propod,
forma prehensile organ. P5 much longer than P6
and P7 in the bispinosa form and only slightly
longer than the other two in the compressa form.
Male. Peduncle of Al 3-segmented; multisegmented flagellum with lst segment bearing two
rows of aesthetaecs. A2longer than Al with multisegmented flagellum.
Remarks
This was the only species sampled at all stations
and was also the most numerically abundant
amphipod in the Straits. Males were rarer than
females in both the bispinosa and compressa
forms. Barnard (1932) also reported a small percentage (2.3 o/o) of males in the population. The
percentage of males sampled in the present study
was 0.70 o/o in the bispinosa form and 12 o/o in the
compressa form. In accordance with Barnard
(1932) and Schneppenheim and WeigmannHaass (1986), we also found a larger number of
bispinosa (77.7 o/o) than compressa (22.3 o/o)
forms. Schneppenheim and Weigmann-Haass
( 1986) report that: "A2 of females and males have
a multisegmented flagellum". This is true only
for males, since females have a single, very long
article, as also shown by the same authors in fig.
1. The male Al consists in a 3-articulate peduncle and a multiarticulate flagellum, contrary to
what is reported by Schneppenheim and Weigmann-Haass (1986) and Ramirez and Viîias
(1985).
Distribution
T. gaudichaudii was considered as having a bipolar distribution (Bowman 1960; Kane 1966; Vinogradov et al. 1982). More recently, Schneppenheim and Weigmann-Haass (1986), on the hasis
of morphological and electrophoretic studies,
have concluded that the species is confined to
Antarctic waters and has a circumpolar distribution. In the Straits of Magellan, it was frequently
sampled at all stations. It is without doubt the
most abundant amphipod in the Straits, from
the Pacific to Atlantic entrances, with a wide distribution range from the surface to maximum
depths.
Themisto gaudichaudii Guerin, 1828: p. 774
Euthemisto gaudichaudii Bovallius, 1889: p. 299,
figs. 1-5, pl. 13 figs. 44-46.
Parathemisto (Euthemisto) gaudichaudii Hurley,
1955: p. 161, figs. 159-174.
Parathemisto gaudichaudii Sheader and Evans,
1974: p. 915 (key) - Sheader, 1975: p. 887 -
Schneppenheim and Weigmann-Haass, 1986: p.
219, figs. 1, la, p. 222 (key).
Body length -
females: 6.4-13.0 mm (30 specimens)
males: 7.0-13.0 mm (30 specimens)
Female. Body keel-like dorsally with strong dorsai spines about ;::: 1 O mm in length. Article 4 of
Al curved. Flagellum of A2 with one article. Anterior extremity ofP2 merus rounded. P3 and P4
with dilated carpus that together with propod,
forma prehensile organ. P5 much longer than P6
and P7 in the bispinosa form and only slightly
longer than the other two in the compressa form.
Male. Peduncle of Al 3-segmented; multisegmented flagellum with lst segment bearing two
rows of aesthetaecs. A2longer than Al with multisegmented flagellum.
Remarks
This was the only species sampled at all stations
and was also the most numerically abundant
amphipod in the Straits. Males were rarer than
females in both the bispinosa and compressa
forms. Barnard (1932) also reported a small percentage (2.3 o/o) of males in the population. The
percentage of males sampled in the present study
was 0.70 o/o in the bispinosa form and 12 o/o in the
compressa form. In accordance with Barnard
(1932) and Schneppenheim and WeigmannHaass (1986), we also found a larger number of
bispinosa (77.7 o/o) than compressa (22.3 o/o)
forms. Schneppenheim and Weigmann-Haass
( 1986) report that: "A2 of females and males have
a multisegmented flagellum". This is true only
for males, since females have a single, very long
article, as also shown by the same authors in fig.
1. The male Al consists in a 3-articulate peduncle and a multiarticulate flagellum, contrary to
what is reported by Schneppenheim and Weigmann-Haass (1986) and Ramirez and Viîias
(1985).
Distribution
T. gaudichaudii was considered as having a bipolar distribution (Bowman 1960; Kane 1966; Vinogradov et al. 1982). More recently, Schneppenheim and Weigmann-Haass (1986), on the hasis
of morphological and electrophoretic studies,
have concluded that the species is confined to
Antarctic waters and has a circumpolar distribution. In the Straits of Magellan, it was frequently
sampled at all stations. It is without doubt the
most abundant amphipod in the Straits, from
the Pacific to Atlantic entrances, with a wide distribution range from the surface to maximum
depths.