ヒシマトウダイ科 Grammicolepididae
Diamond Dories
19
オオヒシマトウダイ
Grammicolepis brachiusculus
Poey, 1873
Thorny Tinselfish
Specimens examined:
2 (
Counts:
D VI, 33–34; A II, 33; P1 14–15; P2 I, 6; GR 1–2+12–13=15;
LLS 100–105; V 10+34=44. Measurements:
head length 25.3–26.6% SL; body depth 53.1–57.2% SL; predorsal
length 36.0–37.7% SL; preanal length 48.4–50.7% SL;
eye diameter 39.2–40.3% HL; interorbital width 31.7–32.6%
HL; snout length 32.2% HL; upper-jaw length 19.4–20.1% HL; postorbital head
length 29.9–30.8% HL; caudal-peduncle depth 27.8–30.1% HL; caudal-peduncle
length 47.1–55.8%; HL; pectoral-fin length 42.1–46.2% HL; pelvic-fin length 64.3–67.3%
HL.
計数形質：背鰭6棘，33–34軟条；臀鰭2棘，33軟条；胸鰭14–15軟条；腹鰭1棘，6軟条；鰓耙数1–2+12–13=15；側線鱗数100–105；脊椎骨数10+34=44．計測形質：頭長25.3–26.6
% SL；体高53.1–57.2
% SL；背鰭前長36.0–37.7
% SL；臀鰭前長48.4–50.7
% SL；眼径39.2–40.3
% HL；両眼間隔31.7–32.6
% HL；吻長32.2
% HL；上顎長19.4–20.1
% HL；眼後頭長29.9–30.8
% HL；尾柄高27.8–30.1
% HL；尾柄長47.1–55.8
% HL；胸鰭長42.1–46.2
% HL；腹鰭長64.3–67.3
% HL．
特 徴 体は高く，琵琶形で，強く側扁する．頭は小さく，頭長は体長の約1/4．吻は短く，尖る．鼻孔は楕円形で，前鼻孔は小さく，後鼻孔は非常に大きい．口は端位で嘴状．両顎に微小な円錐歯が１列に並ぶ．鋤骨に歯がない．眼は大きい．両眼間隔幅は吻長とほぼ同じ．背鰭始部は鰓蓋後縁のやや後方にある．背鰭および臀鰭基底は棘条部で短く，軟条部で長い．背鰭および臀鰭基底に沿って小棘が1列に並ぶ．背鰭棘は細く，第1棘が最長．臀鰭棘は短く，軟条部から離れる．背鰭，臀鰭および胸鰭の軟条は不分枝．腹鰭始部は胸鰭基底下にある．尾柄は細い。尾鰭は大きく、伸長する。体，頬部および鰓蓋部は垂直方向に伸長した細長い鱗で覆われる．体は銀色がかった茶色．尾鰭の鰭膜は黒い。
分 布 南アフリカ，南西インド洋海嶺，オーストラリア，ニュージーランド，ニューカレドニア，日本，台湾，ハワイおよび大西洋の両側の水深400–1026
m (Karrer
and Heemstra, 1988; Nakabo
and Kai, 2013; 本研究)．
備 考 ヒシマトウダイ科は3属3種，すなわち本種，Xenolepidotus delgleishi
Gilchrist, 1922 およびMacrurocyttus acanthopodus
Fowler, 1933（後者は西部太平洋のみから知られる）からなる (Nyako and Amaoka, 1996; Paxton et
al., 2006)．本種は，おおむね同じ海域に出現するX.
delgleishiとは，背鰭棘状が多いこと（通常7，稀に6
vs. 通常6，稀に5），背鰭軟条 (32–34
vs. 27–30) および臀鰭軟条
(33–35 vs. 27–29) が多いこと，成魚の臀鰭棘間に固定機構がないこと（vs.
固定機構がある）で区別できる (Tyler
et al., 2004)．
（篠原）
Description
Body
deep, lute-like and strongly compressed. Head small, its length about 1/4 of
SL. Snout short, pointed. Nostrils elliptical; anterior one small, posterior
one very large. Mouth terminal, beak-like. Minute conical teeth in a single row
on both jaws. No teeth on vomer. Eye large. Interorbital width about equal to snout length. Dorsal-fin
origin slightly behind posterior margin of opercle.
Base of spinous portion of dorsal and anal fins
short, bases of soft portions elongated. Small spines arranged in a single row
along dorsal- and anal-fin bases. Dorsal-fin spines slender, first longest.
Anal-fin spines short, separated from soft rays. Soft rays unbranched
in dorsal, anal and pectoral fins. Pectoral fin small. Pelvic-fin origin below
pectoral-fin base. Caudal peduncle narrow. Caudal fin large, elongated. Body,
cheek and opercle covered with vertically-elongated
scales. Body silvery brown. Caudal-fin membranes black.
Distribution
South Africa, South-West Indian
Ridge, Australia, New Zealand, New Caledonia, Japan, Taiwan, Hawaii and both
sides of the Atlantic Ocean at 400–1026 m depth (Karrer
and Heemstra, 1988; Nakabo
and Kai, 2013; present study).
Remarks
The family Grammicolepididae
is composed of a total of three species in three genera, i.e. G. brachiusculus,
Xenolepidichthys dalgleishi
Gilchrist, 1922 and Macrurocyttus acanthopodus
Fowler, 1934. Grammicolepis brachiusculus
can be separated from X. dalgleishi, which occurs in the same general region, by
having more dorsal-fin spines (usually seven, sometimes six vs. usually six,
sometimes five), more dorsal-fin rays (32–34 vs. 27–30) and anal-fin rays (33–35
vs. 27–29), and no locking mechanism between anal-fin spines in adults (vs. lock
present) (Tyler et al., 2003). Macrurocyttus acanthopodus is
known only from the western Pacific (Nyako and Amaoka, 1996; Paxton et
al., 2006).
(G.
Shinohara)