2. THE SPECIES OF KRILL
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3b. Abdominal segments without dorsal spines.
5a. Lappet a t distal end of first antennular segment produced
beyond mid-point of second segment and flares laterally and
outward, covering upper, outer part of second segment.
Lateral plate (rostrum) does not extend beyond eyes.
6a. Frontal plate (rostrum) in lateral view thin and tapers ;
sometimes rudiments of rostra1 process present. Propodal segment of endopodite of third thoracic leg of
males normal . .
.. .. .. . . aequalis
6b. Frontal plate (rostrum) in lateral view has anterior
margin thickened, fleshy in appearance. Propodal
segment of endopodite of third thoracic leg of male
greatly reduced and dactylus modified as long naked
spine . . .. .. . . ..
subaequalis
5b. Lappet at distal end of basal segment of antennular peduncle
obtusifrons
7a. Superior distal margin of lappet on basal segment of
antennular peduncle pectinate . . .. . . pectinata
7b. Superior distal margin of lappet on basal segment of
antennular peduncle not pectinate.
8a. Dorsal posterior margin of fourth and fifth abdominal
segments very slightly acuminate.
9a. Antennal scale reaches beyond end of second segment
orientalis
9b. Antennal scale reaches to end of second segment
microp ht halrna
8b. Dorsal posterior margin of fourth and H t h abdominal
segments not acuminate. Side plates of abdominal
segments 1-2-3-4 slightly indented on the lower margin
acuti f rons
1 b. Carapace with well-developed cervical groove ; sixth abdominal segment
not produced as far as mid-point of second segment
2b. No lateral denticle on inferior margin of carapace.
shorter than fifth.
l l a . No heavy spines on either side of sixth abdominal segment.
12a. Small, vertical, conical process in centre of frontal margin of
carapace
. . .. .. .. .. . . cornuta
12b. No small conical process in centre of frontal margin of carapace
egregia
l l b . Heavy spine on each side of sixth abdominal segment spinicuudata