36
THE BIOLOGY OF EUPHAUSIIDS
Three species separated by details of
petasma, also on general aspects of body
(Boden et al., 1955)
pseudogibba, paragibba and hemigibba
Id. Species with one pair of lateral denticles on carapace. A well-developed
dorsal process on the third abdominal segment ; conspicuous dorsal
denticles or processes on the fourth and fifth segments.
21a. Hepatic spine on carapace.
22a. Lappet on first antennular segment multidigitate
22b. Lappet on first antennular segment bifid. .
spinifera
. . hanseni
21b. No hepatic spine on carapace.
23a. Posterior margin of the third to fifth abdominal somites
incised. Lateral denticles of the carapace situated above the
margin. Antennular lappet bifid . . ..
longirostris
23b. Posterior margin of the third to fifth abdominal somites entire.
Lateral denticles of the carapace marginal. Antennular lappet
.. .. . . triacantha
bifid . . .. .. I .
Genus Tessarabrachion
Carapace with frontal plate small, triangular, short and much
broader than long; no rostra1 process. Eyes very large, higher than
broad, constricted not much above the middle. Second and third pairs
of thoracic limbs elongated. Three following pairs have normal
endopods ; sixth pair with exopod normally developed, while endopod
in female with two segments, very slender and slightly longer than the
exopod ; no exopod in male. Eighth pair without endopod in both sexes,
while the somewhat small exopod is one-segmented, filiform.
One species only . . .. .. .. .. . . oculatum
Genus Nematoscelis
This group is very difficult to identify, especially the two species
N . microps and N . atlantica. Ruud (1936) uses an index of eye size
against carapace length (Fig. 8) to discriminate these species. Most of
the other species are fairly easily identified from an examination of the
petasma in males.
la. Second pair of thoracic legs with long spines from terminal segment and
from distal end of preceding segment. Third to sixth thoracic legs with
three segments beyond knee. Rostrum downward curved, obtuse, or
lacking. Eye large, with lower part larger than upper. Adults 20-26 mm
in length.
THE BIOLOGY OF EUPHAUSIIDS
Three species separated by details of
petasma, also on general aspects of body
(Boden et al., 1955)
pseudogibba, paragibba and hemigibba
Id. Species with one pair of lateral denticles on carapace. A well-developed
dorsal process on the third abdominal segment ; conspicuous dorsal
denticles or processes on the fourth and fifth segments.
21a. Hepatic spine on carapace.
22a. Lappet on first antennular segment multidigitate
22b. Lappet on first antennular segment bifid. .
spinifera
. . hanseni
21b. No hepatic spine on carapace.
23a. Posterior margin of the third to fifth abdominal somites
incised. Lateral denticles of the carapace situated above the
margin. Antennular lappet bifid . . ..
longirostris
23b. Posterior margin of the third to fifth abdominal somites entire.
Lateral denticles of the carapace marginal. Antennular lappet
.. .. . . triacantha
bifid . . .. .. I .
Genus Tessarabrachion
Carapace with frontal plate small, triangular, short and much
broader than long; no rostra1 process. Eyes very large, higher than
broad, constricted not much above the middle. Second and third pairs
of thoracic limbs elongated. Three following pairs have normal
endopods ; sixth pair with exopod normally developed, while endopod
in female with two segments, very slender and slightly longer than the
exopod ; no exopod in male. Eighth pair without endopod in both sexes,
while the somewhat small exopod is one-segmented, filiform.
One species only . . .. .. .. .. . . oculatum
Genus Nematoscelis
This group is very difficult to identify, especially the two species
N . microps and N . atlantica. Ruud (1936) uses an index of eye size
against carapace length (Fig. 8) to discriminate these species. Most of
the other species are fairly easily identified from an examination of the
petasma in males.
la. Second pair of thoracic legs with long spines from terminal segment and
from distal end of preceding segment. Third to sixth thoracic legs with
three segments beyond knee. Rostrum downward curved, obtuse, or
lacking. Eye large, with lower part larger than upper. Adults 20-26 mm
in length.