2. THE SPECIES O F KRILL
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2a. Lappet of first antennular segment pectinate.
3a. Second antennular segment, distal end dorsally with no tubercles
americuna
3b. Second antennular segment, distal end dorsally with two
tubercles.
4a. Terminal process of petasma bearing a slender spiniform
process toward the tip; process on the proximal process
evenly curved
. . .. .. .. . . eximia
4b. Terminal process of petasma without spine ; process on the
proximal process trifid . . .. .. . . krohnii
2b. Lappet on first antennular segment not pectinate.
5a. No processes on second antennular segment
. . mutica
5b. One spine, on outer distal margin only of second antennular
brevis
5c. Second antennular segment, distal end dorsally with two
tubercules. Male and female with the lappet on the first antennular segment bifid and forward pointing . .
diomedeae
5d. Second antennular segment, distal end dorsally with a spine and
tubercles. Male with reflexed simple lappet on fist antennular
segment, this lappet bifid and upstanding in female
recurva
lb. Species with one pair (rarely none) of lateral denticles on the carapace.
No dorsal process generally on third abdominal segment but sometimes a
small spinous process, sometimes a dorsally produced localized keel.
6a. Hind margins of first and second abdominal segments straight
segment. Male and female with lappet on antennule bifid
dorsally.
7a. Distal segment of the mandibular palp, long and slender
7b. Distal segment of the mandibular palp, short and broad.
superba
8s. Antennular lappet developed in both male and female.
9a. Antennular lappet well developed and forming an
anteriorly broadly rounded plate. The rostrum a short,
sharp triangle . . .. .. .. . . vallentini
10a. Antennular lappet small but conspicuous, about as
broad as long and protruding forwards and
upwards. The rostra1 plate, as a rule, is a distinct
low triangle, broader than long to nearly rudimentary . . .. .. .. . . lucens
9b. Antennular lappet small and triangular.