タチウオ科　Trichiuridae          Cutlassfishes

 

39 オビレタチ
Lepidopus caudatus (Euphrasen, 1788)     Silver Scabbardfish

 

Specimens examined: 6 (SNFR 16233–16237, 17885; 1152–1313 mm SL), 134–520 m depth.

Counts: D III, 98–101; A I, 58–65; P₁ 12; GR 11–18+23–29=35–47; Dorsal-fin soft rays behind first anal-fin spine 38–39; V 40+70=110. Measurements: head length 15.0–16.3% SL; body depth 7.4–7.9% SL; eye diameter 18.8–20.7% HL; snout length 37.5–39.7% HL; interorbital width 15.3–18.4% HL; upper-jaw length 36.0–38.9% HL; lower-jaw length 55.7–60.9% HL; caudal-peduncle length 1.3–2.2% SL; caudal-peduncle depth 0.5–0.8% SL; longest pectoral-fin length 7.1–7.3% SL.

 

計数形質：背鰭3棘，98–101軟条；臀鰭1棘，58–65軟条；胸鰭12軟条；鰓耙数11–18+23–29=35–47；脊椎骨数40+70=110．計測形質：頭長15.0–16.3% SL；体高7.4–7.9% SL；眼径18.8–20.7% HL；吻長37.5–39.7% HL；両眼間隔15.3–18.4% HL；上顎長36.0–38.9% HL；下顎長55.7–60.9% HL；尾柄長1.3–2.2% SL；尾柄高0.5–0.8% SL；胸鰭最長軟条長7.1–7.3% SL．

特　徴　体は細長く，側扁し，リボン状を呈する．2叉する小さい尾鰭をもつ．頭は大きく，両眼間域はわずかに凹む．口は大きく，開口時に突出しない．上顎後端は眼の前縁下に達する．下顎の先端は上顎の先端を超える．両顎の先端に肉質の小突起がある．鼻孔は1個で長半円形．上顎先端に逆棘のない牙状歯が2–3対ある．下顎先端に牙状歯はない．両顎の側面に約30本ずつの犬歯状歯が1列に並び，上下の顎で大きさに差はない．鋤骨に歯はなく，口蓋骨に1列の小歯がある．鰓耙は鋭い棘状で，第1鰓弓隅角部のものは他のものより小さい．側線は１本で，鰓蓋上縁部に発し徐々に下降しつつ，体中央部より後ろでは体側面のやや腹方を直線状に走り，尾鰭基部に達する．腹鰭はごく小さく，鱗状を呈する．側線鱗を除くと無鱗．体色は一様に銀白色で，尾鰭は黒褐色を帯び，他の鰭は白い．口腔内は黒い．

分　布　北太平洋を除く全世界の温帯域 (Nakamura and Parin, 1993)．

備　考　本種はハワイ海嶺に生息する同属近縁種L. calcar Parin and Mikhailin, 1982に似るが，第2臀鰭棘が板状で瞳孔より短い（vs. L. calcarではけづめ状で瞳孔より長い）こと，背鰭条数が98–110であること，臀鰭軟条数が59–66 (vs. 44–47)であること，全脊椎骨数が105–114 (vs. 98–100) であることでから識別できる（Nakamura and Parin, 1993）．

（日��）

 

Description  Body extremely elongated, strongly compressed. Small forked caudal-fin present. Head large, with flat interorbital region. Mouth large, not protractile when opened. Posterior margin of maxilla reaching to anterior margin of eye. Lower jaw extending anteriorly beyond upper jaw. Dermal processes present at tips of upper and lower jaws. Single nostril elongate, crescentic. Two or three pairs of large fangs at front of upper jaw. Fangs absent from lower jaw. About 30 strong canine teeth in a series in each jaw; upper- and lower-jaw teeth subequal in size. No teeth on vomer and small uniserial teeth on palatine. Gill rakers on first gill arch sharp and spinescent; a raker at corner smaller than others. A single lateral line, descending gradually from upper margin of opercle to slightly below mid-line at about mid-body, thereafter straight to caudal-fin base. Pelvic fin tiny, scale like. Body naked except for tubular lateral-line scales. Body uniformly silvery white. Caudal fin blackish brown, other fins white. Oral cavity black.

Distribution  Circumglobal in warm seas except northern Pacific (Nakamura and Parin, 1993).

Remarks  This species is most similar to its congener, Lepidopus calcar Parin and Mikhailin 1982 (Hawaiian Submarine Ridge), but can be distinguished by having the plate-like second anal-fin spine shorter than the pupil (vs. spur-like and longer than pupil in L. calcar), dorsal-fin elements 98–110 (vs. 91–93), anal-fin soft elements 59–66 (vs. 44–47), and total vertebrae 105–114 (vs. 98–100) (Nakamura and Parin, 1993).

(K. Hidaka)