The Isopods of Abyssal Depths in the Atlantic Ocean

128 ROBERT J. MENZIES
seen specimens of Pseudomesus and therefore hesitate to
make that assignment.
Genus: MACROSTYLIS G. O. Sars, 1863
Type species: Macrostylis spinifera G. O. Sars, 1863,
p. 15.
Diagnosis: Macrostylidae with the fourth peraeopods
shorter than the others. Uropoda elongate.
First three peraeonal somites almost fused into a
single unit.
Composition: Although Wolff (1956) correctly
indicates that ten species are known from the genus,
he omitted M. spinifera from his key to the species.
In depth the species range from the shallow water of
Christiania Fjord to the floor of the Philippine trench
at 10,000 meters. Here eight additional species are
described from the abyssal Atlantic, where previously
only one abyssal species was known.
The uropods are terminal and two-jointed in
Macrostylis, and above them there is often a deep
notch in the dorsum of the pleon. The uropoda are
not dorsal in insertion as shown by Wolff, 1956,
p. 100, Fig. 13, but terminal.
THE KNOWN SPECIES OF MACROSTYLIS
Species
1. spiniceps Barnard
2. longipes Hansen
3. subinermis Hansen
4. longiremis (Meinert)
5. elongata Hansen
6. hadalis Wolff
7. galatheae Wolff
8. latifrons Beddard
9. abyssicola Hansen
0. spinifera G. O. Sars
Depth Range {Meters)
Least Greatest
—
—
1090
149
—
—
9820
—
3229
4
1280
1412
1902
218
1591
7270
10,000
3749
3521
1761
A KEY TO THE SPECIES OF MACROSTYLIS
1. Apical margin of pleon with conspicuous setae . 2
1. Apical margin of pleon without conspicuous
setae 8
2. Postero-lateral margins of fourth peraeonal somite
pointed and projecting 3
2. Postero-lateral margins of fourth peraeonal somite
evenly rounded 4
3. Uropodal peduncle longer than
pleon hirsuticaudis, n. sp.
3. Uropodal peduncle not as long as pleon . . . . 5
4. Postero-lateral angles of peraeonal somites 5-7
with a stout seta 6
4. Postero-lateral angles of peraeonal somites
5-7 without stout spine longipes Hansen
5. Peduncle of uropods longer than greatest
width of pleon spinifera (G. O. Sars)
5. Peduncle of uropods shorter than greatest width of
pleon longiremis (Meinert)
6. Fourth somite of peraeon narrower than third
and fifth somites setifer, n. sp.
6. Fourth peraeonal somite as wide as third and
fifth
7. Postero-lateral angles of cephalon
7
sharply pointed
7. Postero-lateral angles of cephalon
caribbkus, n. sp.
evenly rounded
8. Medial apex of pleon
subinermis Hansen
emarginate bifurcatus, n. sp.
8. Medial apex of pleon convex or truncated, never
bifurcated 9
9. Apex of pleon truncated truncatex, n. sp.
9. Apex of pleon pointed or rounded 10
10. Cephalon wider than peraeon with posterolateral
angles projecting spiniceps Barnard
10. Cephalon not wider than peraeon, postero-lateral
angles not projecting beyond peraeonal margin . 11
11 Pleon with bulbous swellings at uropod
insertion making the pleon appear
constricted cephalad of uropods . . . . vemae, n. sp.
11 Pleon not swollen laterally in front of uropod
insertion 12
12 First and second peraeonal somites subequal in
length 13
12 First peraeonal somite much shorter or longer than
second 14
13. Cephalon quadrate in shape, as wide in
13
14
14.
15.
front as behind abyssicola Hansen
Cephalon narrower in front than behind . . . . 15
First peraeonal somite much shorter than
second minutus, n. sp.
First peraeonal somite much longer than
second . hadalis Wolff
Cephalon narrower than peraeon 17
15. Cephalon as wide as peraeon 16
16. Postero-lateral angles of cephalon rounded,
lacking setae galatheae Wolff
16. Postero-lateral angles of cephalon pointed
with stout seta at apex bipunctatus, n. sp.
17. Pleon with statocysts elongata Hansen
17. Pleon without statocysts latifrons Beddard
Macrostylis truncatex, new species
Figure 27 A-G
Synonyms: None.
Diagnosis: Cephalon narrower in front than rear,
front rounded. Fourth peraeonal somite as wide as
third and fifth, lateral borders rounded. First
peraeonal somite slightly longer than second. Uropodal
peduncle not longer than pleon width; dorsum
of pleon with a pair of carinae in front of uropods, pits
and sensory organs lacking, apical border truncated
lacking plumose setae. Apex of male first pleopods
simple, rounded, without stout spines or lateral projections
but with nine setae. First antenna with fivearticles
(male).
Measurements: Holotype male length 3.5 mm.,
width pleon 0.6 mm.
Type locality: North Atlantic, L.G.O. Biotrawl
No. 246, one male, cat. no. 1-117.
Distribution: Known only from type locality.
Affinities: The truncated nature of the pleonal
apex distinguishes this species.