ハチビキ科 Emmelichthyidae Rovers
32 ナンヨウハチビキ
Plagiogeneion rubiginosum
(Hutton, 1875) Rubyfish
Specimens
examined: 8 (
Counts:
D XII, 10–11; A III, 10; P1 20–22; P2 I, 5; GR 11–13+26–29=37–41;
LLS 65–70; V 10+14=24. Measurements: head
length 26.9–31.2% SL; body depth 28.0–32.5% SL; eye diameter 27.1–36.4% HL; interorbital width 26.9–33.4% HL; snout length 25.2–27.8%
HL; upper-jaw length 39.8–44.0% HL; lower-jaw length 43.9–51.2% HL;
caudal-peduncle length 64.3–79.0% HL; caudal-peduncle depth 24.8–29.6% HL;
pectoral-fin length 73.1–88.5% HL; pelvic-fin length 50.8–64.7% HL.
計数形質：背鰭12棘，10–11軟条；臀鰭3棘，10軟条；胸鰭20–22軟条；腹鰭1棘，5軟条；鰓耙数11–13+26–29=37–41；側線鱗数65–70；脊椎骨数10+14=24．計測形質：頭長26.9–31.2%
SL；体高28.0–32.5% SL；眼径27.1–36.4% HL；両眼間隔26.9–33.4% HL；吻長25.2–27.8% HL；上顎長39.8–44.0%HL；下顎長43.9–51.2% HL；尾柄長64.3–79.0% SL；尾柄高24.8–29.6% HL；胸鰭長73.1–88.5% HL；腹鰭長50.8–64.7% HL.
特 徴 体は伸長し，やや側扁する．両眼間隔は口を閉じるとゆるい凸面，口を開くと楕円形に凹む．尾柄長は尾柄高の約2.5倍．口は斜めで，突出させると円筒形になる．上顎後端は眼の前縁を超える．両顎前部に1–2列の微小な円錐歯がある．鋤骨，口蓋骨に歯はない．上唇直後の吻部正中線上にU字形の浅い凹みがある．鰓腔の後縁に肉質突起はない．鰓耙は長く密生する．主鰓蓋骨の後縁に平坦な2棘がある．側線はゆるく湾曲する．鱗は櫛鱗．頭部は唇および上唇の直後を除き鱗に覆われる．背鰭および臀鰭の基部は小鱗からなる鱗鞘に覆われる．体の鱗は尾鰭中央部に延びる．背鰭の棘条部と軟条部は連続し，軟条部の前方で僅かにくぼむ．臀鰭基底長は尾柄長より僅かに短い．背鰭および臀鰭の最終軟条は伸長しない．尾鰭は二叉する．腹鰭間棘はごく短い．体および頭部は淡紅色で，背面で褐色を帯び，腹面で銀色を帯びる．鰭は赤みを帯びる．尾鰭後端は黒みを帯びる．小型個体（180
mm SL以下）では背面に淡褐色の鞍状斑が5本ある．
分 布 ニュージーランド，オーストラリア，南アフリカ，南インド洋のセントポール島およびアムステルダム島，南大西洋のベマ海山，南西インド洋海嶺 (Heemstra and Randall,
1977; present study)．
備 考 南インド洋には同属のPlagiogeneion
macrolepis
McCulloch, 1914（オーストラリア南部）および Plagiogeneion
fiolenti Parin, 1991 (マダガスカル島南方740
km に位置する海嶺 Walters
Shoals)が分布する
(Parin, 1991)．ナンヨウハチビキは，P. macrolepisとは側線鱗数が多いこと(65–74
vs. 48–51)，P.
fiolenti とは主鰓蓋骨の後縁に2棘をもつこと（P. fiolenti
では1棘）で区別できる (Heemstra and Randall, 1977; Parin,
1991; 本研究)．
(星野)
Description
Body
elongated, moderately compressed. Interorbital space
slightly convex when mouth closed, but elliptically concave when mouth open.
Caudal peduncle about 2.5 times longer than deep. Mouth oblique, cylindrical
when protruded. Upper jaw extending posteriorly
beyond a vertical through anterior margin of eye. One or two rows of minute
conical teeth anteriorly in both jaws; vomer, and palatine toothless. Shallow, U-shaped, notch
just behind upper lip on midline of snout. No fleshy protuberance on rear
margin of gill cavity. Gill rakers long, dense. Opercle with two flat spines on posterior margin. Lateral
line gently arched. Scales ctenoid. Head fully scaled
except lips and area just behind upper lip. Bases of dorsal and anal fins
covered with sheath of small scales. Scales of body continuing onto middle part
of caudal fin. Spinous and soft-rayed portions of
dorsal fin continuous, slightly notched before soft-rayed part. Anal-fin base
slightly shorter than caudal peduncle. Last dorsal- and anal-fin rays not
prolonged. Caudal fin forked. Interpelvic spine very
short. Body and head rosy pink, brownish dorsally, silvery ventrally. Fins
reddish; tips of caudal fin blackish. Five saddle-like light brownish bars
present on back in small (ca. 180 mm or smaller) specimens.
Distribution New
Zealand, Australia, South Africa, St. Paul and Amsterdam islands (South Indian
Ocean), Vema Seamount (South Atlantic Ocean),
South-West Indian Ridge (Heemstra and Randall, 1977;
present study).
Remarks
Two congeners, Plagiogeneion macrolepis McCulloch, 1914 (from
southern
(K.
Hoshino)