The Isopods of Abyssal Depths in the Atlantic Ocean

Distribution: Known also from the South Atlantic,
from L.G.O. Biotrawl No. 53, one female, cat. no.
1-204, and from L.G.O. Biotrawl No. 212, one female,
cat. no. 1-74.
Affinities: This species is close to S. spinulosus, from
which it differs in lacking spines from the uropodal
peduncle.
Stylomesus productus, new species
Figure 26 A-C
Synonyms: None.
Diagnosis: Stylomesus with three fused pleonal
somites. Uropodal peduncle extending far beyond
apex of pleon. Dorsum of pleon with two pits, one at
apex, one in front of apex. Apex of male first pleopod
with seven setae and lateral expansions. Lateral
margin male first pleopods with two large swellings
just behind apex. Seventh peraeonal somite not
separated from pleon.
Measurements: Length last six somites (inclusive of
pleon) 3.0 mm., width pleon 0.6 mm.
Type locality: South Atlantic, L.G.O. Biotrawl
No. 214, type male fragment only, cat. no. 1-214.
Distribution: Known only from type locality.
Affinities: This species is near to S. simulans, but
differs in having an additional lobe along the lateral
border of the male first pleopods at its distal half.
Stylomesus simulans, new species
Figure 26 D-F
Synonyms: None.
Diagnosis: Stylomesus with three fused pleonal
somites. Uropodal peduncle just extending beyond
apex of pleon. Dorsum of pleon with two pits, one at
apex, one in front of apex. Apex of each male first
pleopod with seven setae and lateral expansions.
Lateral margins male first pleopod with only one
swelling just behind apex. Seventh peraeonal somite
fused with pleon.
Measurements: Length male last five somites 1.9
mm., width pleon 0.7 mm.
Type locality: South Atlantic, L.G.O. Biotrawl
No. 214, type only, cat. no. 1-243.
Distribution: Known only from type locality.
Affinities: This species resembles S. productus
Type genus: Macrostylis G. O. Sars, 1863.
Diagnosis: Paraselloidea with free first peraeonal
somite. Mandible with pointed molar bearing setae
at apex; palp lacking. First three articles of maxillipedal
palp as wide as endite, last two narrow, small.
Uropoda styliform; uniramous. First pair of antennae
shorter than peduncle of second pair of antennae.
ABYSSAL ATLANTIC ISOPODS 127
Family: MACROSTYLIDAE
Figure 26. A-C: Stylomesus productus, n. sp.
A: dorsal view male (minus cephalon); B:
first male pleopod; C: male pleopod.
D-F: Stylomesus simulans, n. sp. D: dorsal
view male fragment; E: first male pleopod; F:
first male pleopod.
rather closely, but has only one lobe instead of two
along lateral margin of the male first pleopods at its
distal half.
Stylomesus species indeterminable
Indeterminate species of Stylomesus were taken in
L.G.O. Biotrawl No. 12, two fragments, and L.G.O.
Biotrawl No. 47, two fragments.
All peraeopods ambulatory. Pleon consisting of a
single somite only. Anus separated from branchial
chamber.
Composition: This family contains only one genus,
Macrostylis. It is quite possible that Pseudomesus Hansen
should be referred to this family, and in that event
the Pseudomesidae should be canceled. I have not