34
THE BIOLOGY OF EUPHAUSIIDS
lob. Antennular lappet a very small, triangular lobe,
distinctly broader than it is long, the dorsal keel of
the third antennular segment in side view lower
than in E. lucens, with the upper margin straight
and the distal angle nearly rectangular. Rostral
plate as in E. lucens . . .. . . frigida
1Oc. Antennular lappet produced into a triangulate,
dentate process (set obliquely) that projects over
the second segment. Rostral plate barely produced.
These two species differ in form of petasma in males.
E . nana matures at size of 7-3 to 8.5 mm, E. paci$ca
a t 13-24 mm. Lateral denticle on carapace more
anterior in E. paci$cu than in E. nana (Nemoto,
1966). E. nana restricted geographically to sea area
off southern Japan (Brinton, 196213)
paciJicu and nana
8b. Antennular lappet not present in male or female (crystallorophias); not present in male, present as very small
triangular process in female (tenera). Frontal plate produced
to an acute rostrum.
l l a . Eyes, with the cornea wider than the corneal cup.
Length up to 35 mm
.. . . crystallorophias
l l b . Eyes, with the cornea narrower than the corneal cup.
Length up to 10 rnin
.. .. ..
tenera
6b. Hind dorsal margin of the first and second abdominal segments
dorsally with a produced rounded part. Rostrum long and acute,
antennular lappet directed upwards and forwards, bifid, the inner
branch longer than the outer
. . .. .. . . sirnilis
lc. Species with one pair of lateral denticles on carapace. Dorsal surface of
third abdominal segment is produced posteriorly in mid-line, forming
an acute, compressed, spiniform process.
12a. Projection from the dorsal mid-line of the third abdominal segment
varying from a rounded prominence to a short based, truncate keel,
to a short-based spinous keel.
13a. The lappet of antennular segment one, strong bidentate,
projecting over the second segment. Rostrum strongly
projecting
. . .. .. ..
sirnilis var. armata
13b. The lappet of antennular segment one, strong and forming an
anteriorly broadly rounded plate. Rostrum a short, sharp
triangle
. . .. .. .. .. . . vallentini
THE BIOLOGY OF EUPHAUSIIDS
lob. Antennular lappet a very small, triangular lobe,
distinctly broader than it is long, the dorsal keel of
the third antennular segment in side view lower
than in E. lucens, with the upper margin straight
and the distal angle nearly rectangular. Rostral
plate as in E. lucens . . .. . . frigida
1Oc. Antennular lappet produced into a triangulate,
dentate process (set obliquely) that projects over
the second segment. Rostral plate barely produced.
These two species differ in form of petasma in males.
E . nana matures at size of 7-3 to 8.5 mm, E. paci$ca
a t 13-24 mm. Lateral denticle on carapace more
anterior in E. paci$cu than in E. nana (Nemoto,
1966). E. nana restricted geographically to sea area
off southern Japan (Brinton, 196213)
paciJicu and nana
8b. Antennular lappet not present in male or female (crystallorophias); not present in male, present as very small
triangular process in female (tenera). Frontal plate produced
to an acute rostrum.
l l a . Eyes, with the cornea wider than the corneal cup.
Length up to 35 mm
.. . . crystallorophias
l l b . Eyes, with the cornea narrower than the corneal cup.
Length up to 10 rnin
.. .. ..
tenera
6b. Hind dorsal margin of the first and second abdominal segments
dorsally with a produced rounded part. Rostrum long and acute,
antennular lappet directed upwards and forwards, bifid, the inner
branch longer than the outer
. . .. .. . . sirnilis
lc. Species with one pair of lateral denticles on carapace. Dorsal surface of
third abdominal segment is produced posteriorly in mid-line, forming
an acute, compressed, spiniform process.
12a. Projection from the dorsal mid-line of the third abdominal segment
varying from a rounded prominence to a short based, truncate keel,
to a short-based spinous keel.
13a. The lappet of antennular segment one, strong bidentate,
projecting over the second segment. Rostrum strongly
projecting
. . .. .. ..
sirnilis var. armata
13b. The lappet of antennular segment one, strong and forming an
anteriorly broadly rounded plate. Rostrum a short, sharp
triangle
. . .. .. .. .. . . vallentini