440 
PACIFIC SCIENCE, VoL XX, October 1966 
very slender. Setation of legs summarized in 
Table 1. (Willey has illustrated only the endo- 
pod of leg 3, and given only the setation of 
segment 3 of both rami in the text. These agree 
with my Alaskan specimens. Lang (1948:282) 
has included setation for segments 1 and 2 of 
the female exopods and endopods in his Table 
V, although such information is available from 
Willey’s account for only the endopod of leg 3. 
As shown here in Table 1 and in Figure 2, the 
first segment of the exopods of both sexes bears 
a seta, unlike the other species of the genus, 
although D. robusta may have a rudimentary 
seta on exopod 1 in leg 4, if the figure given 
by Sars (1920:P1. 64) is correct. See also com- 
ments above under D. sibirica . ) 
Leg 5 (Fig. 2 E ) . Exopod broader than long, 
with 5 setae, depressed gap between setae 4 and 
5. Basal expansion elongate, reaching beyond 
exopod (longer than in Willey’s Figure 63) ; 
with 5 setae arranged as in figure. 
description of male: Length range — nu- 
wuk lake, 0.94-1.0 mm; chukchi sea coast 
lagoons, 1.0-1. 2 mm. Habitus as in female ex- 
cept that segment bearing leg 5 lacks lateral 
processes, and genital segment is completely 
divided. 
Antennule (Fig. 3). 5-segmented plus a re- 
duced apical part divided into 3 or 4 portions, 
the last clawlike and armed with tuft of 3 or 
more hairlike setae; segments 1-2 usually in- 
completely separated. (Willey states that the 
antennule is as figured by Sars (1909) for D. 
typica, shown as having the same number of 
segments as in my specimens.) Segment 3 sub- 
equal to length of 1 -{— 2, with 10 well-devel- 
oped setae, half of which are plumose; 2 setae 
near outer margin spinelike, set on raised pa- 
pillae, armed with spiculate setules. Segment 4 
presumably with considerable flexibility of outer 
margin permitting contraction or expansion that 
controls, at least in part, movement of expanded 
apical area and its claw; the partial line drawn 
inwards from the margin in Figure 3 is not an 
incomplete segment but a surface line resulting 
from contraction; in less expanded appendages, 
several of these lines may be seen. Segment 5 
greatly enlarged and ornamented (since Figure 
3 has been drawn from dissections studied at 
high magnifications with both dry and oil im- 
mersion objectives, it probably shows details 
common in the genus but not previously illus- 
trated in literature) ; inner margin broken into 
3 processes, the first dentate, the second ridged, 
the last two produced at their distal ends; sur- 
face adjacent to these processes a hollowed area 
from which arise 4 short, plumose setae; this 
area defined by stout, sclerotized ridge begin- 
ning near proximal part of segment, running 
nearly its entire length and ending in stout 
papilla from which an aesthete and 2 setae arise, 
aesthete jointed near distal third; 3 slender, 
closely set setae at base of ridge and a similar 
seta near apex. Number of setae and aesthetes: 
Segment 1 2 3 4 5 
Setae 1 1 10 4 10 
Asthetes 1 
Other cephalic appendages like those of fe- 
male. 
Legs 1-4 (Figs., 2 A, G-L). Inner spine of 
basal segment 2 of leg 1 more slender than 
that of female (Fig. 2 A). Form and setation of 
TABLE 1 
Summary of Setation Legs 1-4 of Danielssenia stefanssoni $ $ * 
SEGMENT 
1 
EXOPOD 
2 
3 
TOTAL 
SEG. 3 
1 
endopod 
2 
3 
TOTAL 
APICAL 
SEG. 
Leg 1 
$ 
$ 
sp-O 
sp-s 
3sp-2s-0 
5 
O-s 
0-sp,2s-s 
4 
Leg 2 
2 
sp-s 
sp-s 
3sp-2s-2s 
7 
O-s 
O-s 
sp-2s-2s 
5 
Leg 2 
$ 
sp-s 
sp-s 
3sp-2s-2s 
7 
O-pr 
pr-O 
0-pr-4s 
4 
Leg 3 
2 
$ 
sp-s 
sp-s 
3sp-2s-3s 
8 
O-s 
O-s 
sp-2s-3s 
6 
Leg 4 
2 
$ 
sp-s 
sp-s 
3sp-2s-3s 
8 
O-s 
O-s 
sp-2s-2s 
5 
* Explanation of symbols: Seg. 7 segment; sp — spine; s — seta, including long, spiniform setae; pr — process. Arrange- 
ment of armature for each segment from outer to inner margin. Position on apical segment shown by the symbol — in- 
dicating outer, apical, and inner margins respectively; or by dividing distinct spines and setae of apex. 
