The Isopods of Abyssal Depths in the Atlantic Ocean

138 ROBERT J. MENZIES
Nannoniscus laevis, new species
Figure 32 D-G
Synonyms: None.
Diagnosis: Nannoniscus with cephalon three times
as broad as the distance between the anterior ends of
the cephalic keels. Antero-lateral angles of first
peraeonal somite with a stout seta; second and third
with a fine seta. Operculum without projecting spines.
Peraeon with two stout recurved spines ventrally.
Fourth article of first antenna extends beyond antennal
vesicle. Pleon without teeth on lateral margins.
Measurements: Holotype female length 3.2 mm.,
width pleon 0.6 mm.
Type locality: South Atlantic L.G.O. Biotrawl No.
53, type and three female paratypes, cat. no. 1-125.
Distribution: Known only from type locality.
Affinities: The blunt lateral borders of the seventh
peraeonal somite distinguish this species from its
nearest relative, N. armatus Hansen.
Nannoniscus primitivus, new species
Figure 32 H-K
Synonyms: None.
Diagnosis: Nannoniscus with cephalon twice as
broad as the distance between the anterior ends of the
cephalic keels. Antero-lateral angles of first peraeonal
somite sharply pointed but without spines; second
with stout spine, third with weak seta. Second article
of first antenna without distal spine-like projections
and third not extending beyond start of vesicle.
Uropodal exopod two-thirds the length of endopod.
Measurements: Holotype male length 1.8 mm.,
width pleon 0.3 mm.
Type locality: North Atlantic, Caribbean, L.G.O.
Biotrawl No. 97, type only, cat. no. 1-178.
Type genus: Eurycope, G. O. Sars.
Diagnosis: Paraselloidea with peraeopods 5-7
inclusive paddle-like, modified for swimming and
bearing dactyls. Cephalon (usually) separated from
first peraeonal somite. Pleon with one or two somites.
Uropoda uni-biramous; peduncle not flattened and
not bearing pulmose setae.
Composition: This family contains Eurycope, Storthyngura,
Syneurycope, Munnopsurus, and Acanthocope.
The genera, except for Munnopsurus, are represented
in the Atlantic abyss and are distinguished from one
another in the following key.
A KEY TO THE GENERA OF THE
EURYCOPIDAE
1. Uropoda biramous 2
1. Uropoda uniramous Acanthocope
Family: EURYCOPIDAE
Distribution: Known only from type locality.
Affinities: This species is unique in the primitive
structure of the first antenna and its vesicle. The
spines on the pleon are probably secondary sexual
characteristics.
Nannoniscus spinicornis Hansen
Figure 32 L-M
Synonyms: Nannoniscus spinicornis Hansen, 1916,
pp. 104-105, PI. X, Figs. 2a-2g.
Diagnosis: Nannoniscus with cephalon twice as
broad as the distance between the anterior ends of the
cephalic keels. Antero-lateral angles of the first three
peraeonal somites only slightly produced, acute, but
without spines or setae. Second and third articles of
first antenna with spine-like projections which extend
to middle of vesicle. Uropodal exopod one-half the
length of endopod.
Measurements: Length of female specimen, 1.5
mm. (Hansen, 1916, p. 104).
Type locality: North Atlantic, South of Jan Ma yen,
Ingolf Station 113, latitude 69° 31'N., longitude
7° 06' W., 2465 meters, temp. —1.0° C, one female
specimen (Hansen, op. cit.).
Distribution: Known only from type locality.
Affinities: This species is close to N. affinis Hansen,
from which it differs in having a wider frontal area to
the cephalon.
Nannoniscus species indeterminable
Damaged specimens of Nannoniscus were taken from
L.G.O. Biotrawl No. 16, three specimens, and L.G.O.
Biotrawl No. 107, one female.
2. Mandibular incisor reduced to a simple
single tooth Munnopsurus
2. Mandibular incisor toothed, normal 3
3. Pleon with lateral spines Storthyngura
3. Pleon without lateral spines 4
4. Inner margin of maxillipedal palp articles
with denticles Syneurycope
4. Inner margin of maxillipedal palp articles
without denticles Eurycope
A LIST OF THE KNOWN ABYSSAL SPECIES OF
EURYCOPE
Depth Range (Meters)
Species Least Greatest
1. hanseni Ohlin 520 2669
2. incisa Gurjanova 2380 2380
3. abyssicola Beddard 3886 3886
4. complanata Bonnier 950 2702