The Isopods of Abyssal Depths in the Atlantic Ocean

96 ROBERT J. MENZIES
18. Medial projection a simple knob 19
18. Medial projection longer than
wide unicornis Menzies
19. Postero-lateral angles of pleon exceed twice
the length of uropoda . . . . retrospinis Richardson
19. Postero-lateral angles of pleon equal the
length of uropoda percavix, n. sp.
20. Lateral border of fourth peraeonal somite
produced forward quadrifrons, n. sp.
20. Lateral border of fourth peraeonal somite not
produced forward 21
21. Uropoda extending almost to the margin of the
postero-lateral angles of the pleon . . . acutus, n. sp.
21. Uropoda very short, less than one-half the
length of the pleon postero-lateral
angles spinifer Hansen
22. Lateral borders of fourth peraeonal somite
produced forward and pointed at antero-lateral
angle elevatus, n. sp.
22. Lateral borders of fourth peraeonal somite not
produced forward or with blunt lateral angles 23
23. Pleon set in from peraeon 27
23. Lateral border of pleon and peraeon
continuous minutus, n. sp.
24. Frontal projection trifid 25
24. Frontal projection entire 26
25. Lateral border peraeon and pleon
continuous tridens, n. sp.
25. Lateral border pleon set in from
peraeon capensis, n. sp.
26. Uropods extending to postero-lateral
margin of pleon nondescriptus, n. sp.
26. Uropods not extending to postero-lateral
margin of pleon princeps, n. sp.
27. Uropods extending beyond postero-lateral
margin of pleon excisus Richardson
27. Uropods not extending to postero-lateral
margin of pleon tropicalis, n. sp.
Haploniscus bicuspis (G. O. Sars)
Figure 6 A-D
Synonyms: Nannoniscus bicuspis G. O. Sars, 1877,
p. 352. Haploniscus bicuspis (G. O. Sars); —
Richardson, 1908a, p. 75; — Hansen, 1916, pp.
29-30, PI. II (incomplete).
Diagnosis: Frontal border of cephalon with a
median projection, base broad tapering to a point.
Flagellum of first antenna with six articles. Lateral
margins of peraeon and pleon continuous. Anterolateral
margin of fourth peraeonal somite not produced
forward, lateral angles blunt. First article of
first antenna not concealed by cephalon dorsally.
Uropods extending to posterior margin of pleon and
to the end of the postero-lateral angles.
Measurements: Length 2.90 mm. (G. O. Sars,
1885, p. 122).
Type locality: North Atlantic, west of Norway,
latitude 63° 5' N., 988 meters (Hansen, 1916, p. 30)
or possibly latitude 69° 46' N., 1220 meters.
Distribution: Hansen (op. cit.) records the species
from 15 Ingolf stations, and one—Station 113, latitude
69°31'N., longitude 7° 06'W., 2465 meters—is
from abyssal depth. Presumably it is eurybathial,
extending from 360 meters to 2465 meters.
Here it is recorded from the South Atlantic,
L.G.O. Biotrawl No. 12, one male and two females,
cat. no. 1-5; and L.G.O. Biotrawl No. 53, one male
and four females, cat. no. 1-4.
It is highly probable that Hansen (op. cit.) confused
at least two species in what he called bicuspis:
his illustrations, PI. II, show specimens in which the
uropoda do and do not reach the posterior margin of
the pleon. For this reason not all of his distributional
data is cited here. I have not seen his specimens.
The male that he figures is doubtless a distinct
bathyal species and probably is identical with Richardson's
retrospinis. It differs from the true bicuspis in
having the apex of the male pleopod swollen and the
uropods not reaching the posterior margin of the
pleon; that is, the postero-lateral angles of the pleon
are much produced.
Affinities: This species is related to tricornis and
tricornoides, from both of which it differs in lacking a
projected base on the medial spine of the frontal
margin of the cephalon.
Haploniscus unicornis Menzies
Figure 6 E-G
Synonym: Haploniscus unicornis Menzies, 1956a, p. 9.
Diagnosis: Frontal border of cephalon convex,
with elongated (longer than breadth of base) spinelike
horn. Lateral borders of pleon and peraeon
continuous. Flagellum of first antenna with five
articles. Postero-lateral angles of pleon produced
beyond medial margin. First article of first antenna
not concealed by cephalon dorsally. Antero-lateral
border of fourth peraeonal somite not produced
forward; lateral margin quadrate. Uropoda extending
beyond apex of pleon but not to tips of posterolateral
angles of pleon.
Measurements: Female length 1.45 mm., width at
second peraeonal somite 0.60 mm. (Menzies, 1956a,
p. 9).
Type locality: North Atlantic, L.G.O. Biotrawl
No. 1, 5104-5122 meters, cat. no. 11759, A.M.N.H.
Distribution: Known only from type locality.
Affinities: The elongate spine which is much larger
than its base on the front of the cephalon distinguishes
this species from the others.
Haploniscus excisus Richardson
Figure 6 H
Synonyms: Haploniscus excisus Richardson, 1908a,
pp. 75-77, Figs. 4-5.
Diagnosis: Frontal border of cephalon excavated,
entire. Flagellum of first antenna with five articles.
Pleon set in from peraeon. Lateral borders of fourth