オオメマトウダイ科Oreosomatidae Oreos
16 ツノマトウダイ
Neocyttus rhomboidalis
Gilchrist, 1906
Spiky Oreo
Specimens examined:
12 (SNFR 16579–16584, 17024–17028; 241–311 mm SL), 396–496 m depth.
Counts:
D VI–VIII, 32–34;
A III–IV, 30–33; P1 19–21; P2 I, 6; GR 3–6+17–22=22–26; LLS
ca. 95–110; V 13–15+25–27=38–41. Measurements:
head length 36.2–39.5% SL; body depth 57.9–72.0% SL; predorsal
length 52.2–61.1% SL; preanal length 60.6–67.1% SL;
eye diameter 42.6–51.1% HL; interorbital width 31.7–37.4%
HL; snout length 25.0–32.5% HL; upper-jaw length 36.5–43.1% HL; postorbital-head
length 32.8–37.8% HL; caudal-peduncle depth 14.7–18.9% HL; caudal-peduncle
length 25.9–34.8% HL; pectoral-fin length 32.8–38.6% HL; pelvic-fin length 41.0–46.7%
HL.
計数形質：背鰭6–8棘，32–34軟条；臀鰭3–4棘，30–33軟条；胸鰭19–21軟条，腹鰭1棘，6軟条；鰓耙数3–6+17–22=22–26；側線鱗数約95–110;
脊椎骨数13–15+25–27=38–41．計測形質：頭長36.2–39.5
% SL；体高57.9–72.0
% SL；背鰭前長52.2–61.1
% SL；臀鰭前長60.6–67.1
% SL；眼径42.6–51.1
% HL；両眼間隔幅31.7–37.4
% HL；吻長25.0–32.5
% HL；上顎長36.5–43.1
% HL；眼後頭長32.8–37.8
% HL；尾柄高14.7–18.9
% HL；尾柄長25.9–34.8
% HL；胸鰭長32.8–38.6
% HL；腹鰭長41.0–46.7
% HL．
特 徴 体は高く，菱形で，側扁する．頭は大きく，眼窩の周囲や両顎および鰓蓋域に骨質板が発達する．背鰭前方の輪郭は凹む．眼は非常に大きく，眼径は頭長の約1/2．眼窩の背前縁は張り出す．両眼間隔域はほぼ平坦．吻は短い．前鼻孔は小さく，卵円形；後鼻孔は大きく，スリット状．口は大きく，突出できる．主上顎骨の前部は涙骨に覆われる．上唇は狭い．両顎と鋤骨に微細な円錐歯がある．下顎後端は尖る．鰓膜は峡部に癒合する．背鰭および臀鰭の基底は棘条部で短く，軟条部で遥かに長い．背鰭第2棘は頑丈で最長．臀鰭第1棘は頑丈で最長．背鰭，臀鰭および胸鰭の軟条は不分枝．胸鰭は小さい．腹鰭棘は頑丈．尾柄は細い．骨質板を除く頭部および体は櫛鱗で覆われる．体は茶色．口腔，鰓膜および各鰭の鰭膜はこげ茶色．
分 布 世界の南緯24–48度の水深290–1320 m（通常は450–800 m）の大陸斜面や海山（Yearsley
and Last, 1998; Bray, 2008）．
備 考 インド洋南西部産のツノマトウダイ属（新称）Neocyttusには本種の他にN. acanthorhynchus
Regan, 1908（マダガスカル島北方）が知られる（Yearsley
and Last, 1998）．本種はN.
acanthorhynchusとは側線鱗が多いこと(88–109
vs. 65–75)で識別できる
(Yearsley and Last,
1998)．ガクガクギョOreosoma atlanticum
Cuvier, 1829とは，鱗が櫛鱗であること（vs.
ガクガクギョは円鱗），眼径が頭長の41–52%と比較的小さいこと (vs.
52–60%)，上唇が狭いこと（vs. 広い）で区別できる．
（篠原）
Description Body
deep, rhomboidal and compressed. Head large, with bony plates developed around
orbit, on jaws and opercular regions. Predorsal profile concave. Eye very large, its diameter
about 1/2 of head length. Dorsoanterior rim of orbit
projected. Interorbital space almost flat. Snout
short. Anterior nostril small, oval; posterior nostril large, slit-like. Mouth
large, protrusible. Maxillary covered by lachrymal anteriorly. Upper lip narrow. Minute conical teeth on both
jaws and vomer. Posterior end of mandible pointed.
Gill membranes united to isthmus. Dorsal and anal fins spinous
portions with very short bases, much shorter than bases of soft-rayed portions;
first spine robust, longest in anal fin; second spine robust, longest in dorsal
fin. Soft rays in dorsal, anal and pectoral fins unbranched.
Pectoral fin small. Pelvic-fin spine robust. Caudal peduncle narrow. Head
except bony plates and body covered with ctenoid scales.
Body brown. Oral cavity, gill membranes and all fin membranes dark brown.
Distribution Circumglobal,
continental slopes and seamounts between latitudes of about 24ºS
and 48ºS at 290–1320 m depth (usually 450–800 m)
(Yearsley and Last, 1998; Bray, 2008).
Remarks One
other congener, N. acanthorhynchus
Regan, 1908 (north of
(G.
Shinohara)