The Isopods of Abyssal Depths in the Atlantic Ocean

5. Antennal squama shorter than the
diameter of third peduncular
article arcticus Hansen
6. Second article of first antenna with process short,
leaving the fourth article uncovered 7
6. Second article of first antenna with long process
overlapping the fourth article 12
7. Posterior ventral area of peraeon without any
process 8
7. Posterior ventral area of peraeon with one or two
large recurved acute processes 9
8. Antennular vesicle two and a half to three
times as long as broad inermis Hansen
8. Antennular vesicle pyriform not one-half
as long again as broad aequiremis Hansen
9. With only one recurved process 10
9. With two
processes armatus Hansen and laevis, n. sp.
10. Posterolateral margin of pleon without incision
or tooth 11
10. Postero-lateral margin of pleon with an
incision and a conspicuous angle or
tooth . . . . minutus Hansen and bidens Vanhoffen
and camayae, n. sp.
11. First peraeopod without stout setae on inferior
margin of (fifth article)
propod plebejus Hansen
11. First peraeopod with two stout setae
on inferior margin of (fifth article)
propod crassipes Hansen
12. Anterior margin of front of cephalon nearly
half as wide as cephalon
width spinicomis Hansen
12. Anterior margin of front of cephalon less than
one-half as wide as cephalon affinis Hansen
LIST OF THE SPECIES OF NANNONISCUS
Species
1. oblongus G. O. Sars
2. simplex Hansen
3. arcticus Hansen
4. analis Hansen
5. laticeps Hansen
6. reticulatus Hansen
7. inermis Hansen
8. aequiremis Hansen
9. plebejus Hansen
10. minutus Hansen
11. armatus Hansen
12. spinicomis Hansen
13. a^nis Hansen
14. australis Vanhoffen
15. bidens Vanhoffen
16. caspius G. O. Sars
17. crassipes Hansen
ABYSSAL ATLANTIC ISOPODS 135
Depth Range (Meters)
Least Greatest
225
1070
75
•—
—•
—
—
—
—
—
—
—
—
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—
Nannoniscus inermis Hansen
Figure 31 A-C
1505
1505
699
2258
552
552
2258
885
1505
1096
3521
2465
1505
385
385
intertidal
?225 468
Synonyms: Nannoniscus inermis Hansen, 1916, pp.
98-99, PI. IX.
Diagnosis: Nannoniscus with cephalon a little more
than four and a half times as broad as the distance
oetween the anterior ends of the cephalic keels.
Antero-lateral angles of first somite of peraeon without
spine; second and third with spine. Tubercle or process
lacking from female operculum, which has a
straight distal margin. Uropodal endopod almost
twice as long as exopod. Pleon without teeth.
Measurements: Female with marsupium length
3.3 mm.
Type locality: North Atlantic, Davis Strait, Ingolf
Station 24, latitude 63° 06' N., longitude 56° 00' W.,
2258 meters, temperature 2.4° C. (Hansen, op. cit.).
Distribution: Known only from type locality.
Affinities: This species seems most nearly related to
N. aequiremis Hansen, differing from it in having a
more elongate antennular vesicle.
Nannoniscus armatus Hansen
Figure 31 D-E
Synonyms: Nannoniscus armatus Hansen, 1916, pp.
102-103, PI. X.
Diagnosis: Nannoniscus with cephalon four times as
broad as the distance between the anterior ends of the
cephalic keels. Antero-lateral angles of first and third
somites without spines on setae. Tubercle or process
lacking from female operculum, which has a convex
distal margin. Uropodal exopod considerably less
than one-half the length of endopod. Pleon without
teeth.
Measurements: Juvenile length 1.6 mm.
Type locality: North Atlantic, south of Davis
Strait, Ingolf Station 38, latitude 59° 12' N., longitude
51° 05' W., 3521 meters, temperature 1.3° C. (Hansen,
op. cit.).
Distribution: Known only from type locality.
Affinities: This species is closely related to N.
laevis, n. sp., differing from it only in having a narrower
frontal area on the cephalon and blunt lateral
borders to the seventh peraeonal somite rather than
angular ones.
Nannoniscus analis Hansen
Figure 31 F-H
Synonyms: Nannoniscus analis Hansen, 1916, pp.
95-96, PI. VIII-IX.
Diagnosis: Nannoniscus with cephalon four times
as broad as the distance between the anterior ends of
the cephalic keels. Antero-lateral angles of first and
third somites with no spines but frequently with a
short seta; second with a distinct long spine. Operculum
with a highly raised strong acute process. Uropodal
endopod not twice as long as exopod. Pleon
without teeth.
Measurements: Large specimen length 2.6 mm.
Type locality: North Atlantic, Davis Strait, Ingolf
Station 24, latitude 63° 06' N., longitude 56° 00' W.,
2258 meters, temperature 2.4° C. (Hansen, op. cit.).
Distribution: Known only from type locality.
Affinities: The concave nature of the pleonal