7.5 Eukrohnia hamata Mobius, 1875
Eukrohnia hamata Mobius, 1875: p. 158, pl. 3
figs. 13-16- von Ritter-Zahony, 1910: p. 268, pl.
5 figs. 11a-b, 12 - Germain and Joubin, 1916: p.
58, pl. 1 figs. 2, 4, pl. 5 figs. 5-13, pl. 8 figs. 6,7 -
Fagetti, 1958a: p. 67, fig. 16a-c- Neto, 1961: p.
46, figs. 38-40 - David, 1958: p. 206 - Ducret,
1965: p. 65, figs. 2, 3a, 4a - Dawson, 1968: p. 116,
fig. 2a-d - Alvarifto, 1969: p. 127, figs. 38a-d,
39a-i- Dinofrio, 1973: p. 18, pl. 1 fig. 5, pl. 2 fig.
5a,b, pl. 3 fig. 5 - pl. 5 fig. 1 - Boltovskoy, 1981: p.
786, fig. 256- Lutschinger, 1993: p. 36, figs 20ad.
Body length -
juveniles: 10-23 mm
Description. Individuals bear only 1 pair of delicate lateral fins. Maximum width of fins at level
of caudal septum, with rays visible only along the
posterior, external border. Anteriorly, fins originate at the level of the midventral ganglion. Posteriorly, fins end at about 2/3 distance separating
distal extremity of tail from the caudal septum.
Length of tail is 19-28 o/o of total length. Body
generally flaccid, but large specimens may appear quite rigid. Commencing from the neck, the
body progressively widens, reaching its maximum width at a distance from the caudal septum
almost equal to the length of the tail. Primary
body musculature well developed, conferring an
opaque colour to the trunk. A thin transversal
musculature is present. The head is small with an
evident neck. There is no presence of alveolar
tissue on the neck (i.e. collarette ). There are 7-11
slightly recurved hooks (5-8 in the Magellan
specimens ), the conical extremities of which are
bent at a right angle with respect to the hook's
main axis. This is a distinctive character for the
genus. The number of teeth varies from 6-26
(Alvarifto 1969), with more teeth occurring in
larger specimens. In our specimens, the number
of teeth varied from 8-18, which more or less coincides with the number reported by von RitterZahony (19llb) for Antarctic specimens and by
Fagetti (1968) for specimens collected off the
Chilean coast. According to Ducret (1965), more
teeth occur in specimens off the African coast
(23-25). Another characteristic feature of the
species are the slightly protruding oval eyes
which lack pigment and bear a small posterior
appendix. Their surface consists of smalllenticular structures similar to 'ommatidia', conferring to the species an aspect reminiscent of the
compound eyes in arthropods. There are no
esophageal diverticulae. Often, the intestine
contains yellowish oily droplets. In mature specimens, the ovaries can be as long as 1/2 the
trunk. The eggs are aligned in 4 rows. The seminal vesicles are oval and do not reach the caudal
fin.
Remarks
According to David ( 1958), the species shows a
great variability in length. In the Southern
Ocean, there are two distinct races that are more
or less separated by the Antarctic Convergence.
Larger individuals have been sampled in Antarctic waters, whereas subtropical specimens seem
to belong to the smaller of the two races. Mature
specimens reach 43 mm in length (Alvarifto
1969; Boltovskoy 1981).
Distribution
The species is epiplanktonic in Arctic and Antarctic regions. In tropical and equatorial areas,
Eukrohnia hamata Mobius, 1875: p. 158, pl. 3
figs. 13-16- von Ritter-Zahony, 1910: p. 268, pl.
5 figs. 11a-b, 12 - Germain and Joubin, 1916: p.
58, pl. 1 figs. 2, 4, pl. 5 figs. 5-13, pl. 8 figs. 6,7 -
Fagetti, 1958a: p. 67, fig. 16a-c- Neto, 1961: p.
46, figs. 38-40 - David, 1958: p. 206 - Ducret,
1965: p. 65, figs. 2, 3a, 4a - Dawson, 1968: p. 116,
fig. 2a-d - Alvarifto, 1969: p. 127, figs. 38a-d,
39a-i- Dinofrio, 1973: p. 18, pl. 1 fig. 5, pl. 2 fig.
5a,b, pl. 3 fig. 5 - pl. 5 fig. 1 - Boltovskoy, 1981: p.
786, fig. 256- Lutschinger, 1993: p. 36, figs 20ad.
Body length -
juveniles: 10-23 mm
Description. Individuals bear only 1 pair of delicate lateral fins. Maximum width of fins at level
of caudal septum, with rays visible only along the
posterior, external border. Anteriorly, fins originate at the level of the midventral ganglion. Posteriorly, fins end at about 2/3 distance separating
distal extremity of tail from the caudal septum.
Length of tail is 19-28 o/o of total length. Body
generally flaccid, but large specimens may appear quite rigid. Commencing from the neck, the
body progressively widens, reaching its maximum width at a distance from the caudal septum
almost equal to the length of the tail. Primary
body musculature well developed, conferring an
opaque colour to the trunk. A thin transversal
musculature is present. The head is small with an
evident neck. There is no presence of alveolar
tissue on the neck (i.e. collarette ). There are 7-11
slightly recurved hooks (5-8 in the Magellan
specimens ), the conical extremities of which are
bent at a right angle with respect to the hook's
main axis. This is a distinctive character for the
genus. The number of teeth varies from 6-26
(Alvarifto 1969), with more teeth occurring in
larger specimens. In our specimens, the number
of teeth varied from 8-18, which more or less coincides with the number reported by von RitterZahony (19llb) for Antarctic specimens and by
Fagetti (1968) for specimens collected off the
Chilean coast. According to Ducret (1965), more
teeth occur in specimens off the African coast
(23-25). Another characteristic feature of the
species are the slightly protruding oval eyes
which lack pigment and bear a small posterior
appendix. Their surface consists of smalllenticular structures similar to 'ommatidia', conferring to the species an aspect reminiscent of the
compound eyes in arthropods. There are no
esophageal diverticulae. Often, the intestine
contains yellowish oily droplets. In mature specimens, the ovaries can be as long as 1/2 the
trunk. The eggs are aligned in 4 rows. The seminal vesicles are oval and do not reach the caudal
fin.
Remarks
According to David ( 1958), the species shows a
great variability in length. In the Southern
Ocean, there are two distinct races that are more
or less separated by the Antarctic Convergence.
Larger individuals have been sampled in Antarctic waters, whereas subtropical specimens seem
to belong to the smaller of the two races. Mature
specimens reach 43 mm in length (Alvarifto
1969; Boltovskoy 1981).
Distribution
The species is epiplanktonic in Arctic and Antarctic regions. In tropical and equatorial areas,