The Isopods of Abyssal Depths in the Atlantic Ocean

90
ROBERT J. MRNZIES
10. Head subcircular, mandibles small and not
extending to margin of frons . . . serrata Richardson
(709 meters, Albatross, N. Atlantic, south of Martha's
Vineyard)
10. Head quadrate, mandibles
normal tuberculata Richardson
(1132 meters, Albatross, 37° 22'.30" N., 137° 47' E.,
off Japan)
11. Peraeopods strongly spinous, head small
(much narrower than peraeon) . . stygia (G. O. Sars)
(535-2391 meters, N. Atlantic)
11. Peraeopods weakly spinous, head large (nearly as
wide as peraeon) 12
12. Somite 4 of peraeon with a sulcus on
dorsal suface at midline caeca Richardson
(2638 meters, N. Atlantic)
12. Somite 4 of peraeon without a sulcus on dorsal
surface at midline 13
13. Lateral border of head strongly convex.
Lateral margin of peraeon convex . . bicolor Hansen
(1537 meters, N. Atlantic)
13. Lateral border of head scarcely convex, borders
of peraeon subparallel albescens Hansen
(842-1018 meters, N. Atlantic)
Genus: GNATHIA Leach
Gnathia vemae, new species
Figure 2
Figure 2. Gnathia vemae, n. sp. A: male holotype;
B: mandible and frons; C: pleotelson
and uropod; D: pylopod; E: frons of praniza;
F: first antenna, male.
Synonyms: None.
Diagnosis: Gnathia with a produced and entire
frons, eyes lacking. Mandible with a pronounced
redan and three teeth. Pylopod with three articles,
last article minute. Flagellum of first antenna with
five articles, second also with five articles. Last two
large peraeonal somites with a dorsal medial sulcus.
Peraeopods not markedly spinous. Pleopoda lacking
setae.
Measurements: Holotype male length 2.8 mm..
width pleotelson 0.2 mm.
Type locality: South Atlantic, L.G.O. Biotrawl No.
55, type plus two male paratypes and one praniza.
cat. no. 1-41.
Distribution: Known only from the type locality.
Affinities: This species is closely allied to Gnathia
caeca Richardson, from which it differs in having teeth
on the mandible; otherwise the two are very similar.
Gnathia caeca Richardson
Figure 3 A-B
Synonyms: Gnathia caeca Richardson, 1911, pp.
519-520; Stephensen, 1915, p. 7; Monod, 1926a,
pp. 406-408.
Diagnosis: Pylopods with three articles. Head as
wide as thorax. Eyes lacking. Frons produced but
not as far as mandible apex. Supraocular lobes
strongly tuberculate. Peraeopods without many stout
spines. Fourth peraeonal somite with a pronounced
dorso-medial sulcus. Margins of uropods and telson
entire, without teeth.
Measurements: Length 5 mm. (Monod, op. cit.,
p. 407).
Type locality: North Atlantic, Talisman Station 76,
latitude 25° 1' N., longitude 19° 15' W., 2638 meters
(Monod, op. cit., p. 408).
Distribution: Known only from type locality.
Affinities: The species appears to be most nearly
related to G. bicolor Hansen in key characteristics at
least [vide Monod, op. cit., p. 332).
Gnathia stygia (G. O. Sars)
Figure 3 C-E
Synonyms: Anceus stygius G. O. Sars, 1877, p.
348; — 1885, pp. 85-92; — 1886, pp. 27, 85. Gnathia
stygius (G. O. Sars), Stebbing, 1893, p. 338; —Ohlin,
1901, p. 22, Fig. 3. Caecognathia stygia (G. O. Sars),
Dollfus, 1901, p. 244. Caecognathia sarsi A. Dollfus,
1901, pp. 244-245, Fig. 3. Bathygnathia stygia (err.
typ.), Stephensen, 1915, p. 6. Caecognathia stygia
(G. O. Sars), Stephensen, 1915, p. 7. Gnathia Stygia
(G. O. Sars), Hansen. 1916, pp. 230-232; Monod,
1926a, pp. 398-405.
Diagnosis: Pylopods with three articles. Head
narrower than thorax. Eyes lacking. Frons produced