2. THE SPECIES OF KRILL
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12b. Projection from the mid-dorsal line of the third abdominal segment
a spinate extension of the region of the dorsal midline of the
segment.
14a. Fourth abdominal segment similarly produced dorsally, but
into a smaller process.
15. Lappet of first antennular segment deeply bifid. Rostrum
short, not produced; lobe absent on the second antennular segment . . .. .. .. . . rnucronata
14b. Fourth abdominal segment not produced dorsally.
16a. Lappet absent on first antennular segment. Lobe also
absent on second antennular segment. Rostrum acute,
very short
. .
..
.. .. . . sibogae
16b. Lappet present, but rudimentary, on first antennular
segment.
17. Lappet rudimentary, plate-like, shallowly incised in
centre. Rostrum very small, acute. Second antennular segment with a small ear-like lobe
dist inguenda
18a. Lappet projecting, roundly cleft a t front end. The
second antennular segment ends in a large rounded
lamella covering half of the third segment; no
rostrum . . .. .. ..
larnelligera
1Gc. Lappet well defined on first antennular segment.
18b. Lappet projecting, pointed.
19a. Lobe absent on second antennular segment.
The spine of the third abdominal segment
compressed and short, acute, at its base a
carinated plate. Rostrum short, very acute
gibba
20a. Lobe of second antennular segment projecting, sub-rectangular, short and
broad. Third antennular segment has
high pointed keel. Rostrum small, but
produced, pointed.
Three species
separated by details of petasma (Brinton,
196%)
gibboides, fallax and sanzoi
20b. Lobe of second antennular segment
represented only by a small sharp tooth.
Third antennular segment has low keel.
19b. Lobe present on second antennular segment.