ハチビキ科 Emmelichthyidae Rovers
31 ホソチビキ
Emmelichthys nitidus
Specimen
examined: 2 (
Counts:
D XIII, 10; A III, 10; P1 21–22; P2
I, 5; GR 10–11+30=40–41; LLS 97–98; V 10+14=24.
Measurements: head length 27.5–27.7%
SL; body depth 21.0–21.1% SL; eye diameter 22.1–22.7% HL; interorbital
width 24.3–28.0% HL; snout length 28.7–29.3% HL; upper-jaw length 40.3–40.6%
HL; lower-jaw length 37.9–38.5% HL; caudal-peduncle length 60.8–65.1% HL;
caudal-peduncle depth 21.3–22.3% HL; pectoral-fin length 68.1–68.6% HL; pelvic
fin-length 43.3–45.8% HL.
計数形質：背鰭13棘，10軟条；臀鰭3棘，10軟条；胸鰭21–22軟条；腹鰭1棘，5軟条；鰓耙数10–11+30=40–41；側線鱗数97–98；脊椎骨数10+14=24．計測形質：頭長27.5–27.7%
SL；体高21.0–21.1% SL；眼径22.1–22.7% HL；両眼間隔24.3–28.0% HL；吻長28.7–29.3% HL；上顎長40.3–40.6%HL；下顎長37.9–38.5% HL；尾柄長60.8–65.1% SL；尾柄高21.3–22.3% HL；胸鰭長68.1–68.6% HL；腹鰭長43.3–45.8% HL.
特 徴 体は伸長し，紡錘形で，体幅は体高の約70%．両眼間隔には浅く大きい楕円形の凹みがある．尾柄は細い．口は斜めで，突出させると円筒形になる．上顎後端は眼の中央下方に達しない．ふつう数本の微小な円錐歯が下顎前部にある．上顎，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2個の肉質突起がある．鰓耙は長く密生する．主鰓蓋骨の後縁には平坦な2棘がある．側線は体背縁にほぼ平行に走る．鱗は櫛鱗．頭部は，唇，眼窩縁辺および吻部前半部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．背鰭棘条部は軟条部と明瞭に分離し，間にある3本の棘は鰭膜により他の棘と連続しない．臀鰭基底長は尾柄長より短い．背鰭および臀鰭の最終軟条は伸長する．尾鰭は二叉する．胸鰭は短い．腹鰭は胸鰭より短い．腹鰭間棘がある．体および頭部は背面で赤褐色，腹面で赤みを帯びた銀色．鰭は赤みを帯びる．
分 布 ニュージーランド，オーストラリア南部，南アフリカ南岸，インド洋南部のセントポール島およびアムステルダム島，南西インド洋海嶺 (Heemstra and Randall,
1977; 本研究)．
備 考 ホソチビキEmmelichthys nitidusはハチビキ科の他種とは，背鰭棘条部と軟条部が明瞭に離れること（ロウソクチビキ属Emmelichthysの特徴）および側線鱗数が87–98であることで区別できる．チリ沖に分布するフンボルトハチビキEmmelichthys cyanescens
(Guichenot, 1848)（かつて本種の別亜種E. nitidus
cyanescens
とされていた）では側線鱗数が100–105と本種より多く，他の本属魚類では85以下と少ない (Heemstra and Randall, 1977; Fricke et al., 2014)．
(星野)
Description
Body
elongate, fusiform, width about 70% of depth. Interorbital space with a shallow, large elliptical concavity.
Caudal peduncle slender. Mouth oblique, cylindrical when protruded. Upper jaw
not reaching posteriorly to a vertical through mid-eye.
Several minute conical teeth usually present at anterior of lower jaw; upper
jaw, vomer, and palatine toothless. Shallow, U-shaped
notch just behind upper lip on midline of snout. Two fleshy protuberances on
rear margin of gill cavity. Gill rakers long, dense. Opercle with two flat spines on posterior margin. Lateral
line approximately parallel to dorsal contour of body. Scales ctenoid. Head fully scaled except lips, margin of orbit,
and anterior half of snout. Bases of dorsal and anal fins covered with sheath
of small scales. Scales of body continuing onto middle part of caudal fin. Spinous dorsal fin separated from soft dorsal fin by a
distinct gap, which contains short, isolated (not connected by membrane)
spines. Anal-fin base shorter than caudal peduncle. Last dorsal- and anal-fin
rays prolonged. Caudal fin forked. Pectoral fin short. Pelvic fin shorter than
pectoral fin; interpelvic spine present. Body and
head reddish brown dorsally, reddish silver ventrally. Fins reddish.
Distribution
Remarks Emmelichthys nitidus can be distinguished from other species of the
family by having the spinous dorsal fin separated
from the soft dorsal fin by a distinct gap (a generic character of Emmelichthys),
and 87–98 lateral-line scales. Emmelichthys cyanescens (Guichenot, 1848),
which used to be classified as a subspecies of the same species (as E. n. cyanescens)
distributed off
(K.
Hoshino)