ムカシクロタチ科　Scombrolabracidae                           Longfin Escolars

 

36 ムカシクロタチ
　Scombrolabrax heterolepis Roule, 1921                        Longfin Escolar

 

Specimens examined: 2 (SNFR 15928, 15929; 162–243 mm SL), 524–852 m depth.

Counts: D XII-I, 13–14; A II–III, 15–16; P₁ 18–19; P₂ I, 5; GR 8–12+5–6=14–17; LLS 47–49; V 13+17=30. Measurements: head length 31.6–32.8% SL; body depth 20.0–22.5% SL; eye diameter 30.9–31.5% HL; snout length 29.1–30.2% HL; interorbital width 26.8–27.4% HL; upper-jaw length 46.4–47.7% HL; lower-jaw length 40.5–47.2% HL; caudal-peduncle length 13.1% SL; caudal-peduncle depth 6.9–7.2% SL; longest pectoral-fin ray length 32.7–35.9% SL; longest pelvic-fin ray length 9.6–12.4% SL.

 

計数形質：背鰭12棘-1棘，13–14軟条；臀鰭2–3棘，15–16軟条；胸鰭18–19軟条；腹鰭1棘，5軟条；鰓耙数8–12+5–6=14–17；側線鱗数47–49；脊椎骨数13+17=30．計測形質：頭長31.6–32.8% SL；体高20.0–22.5% SL；眼窩径30.9–31.5% HL；吻長29.1–30.2% HL；両眼間隔26.8–27.4% HL；上顎長46.4–47.7% HL；下顎長40.5–47.2% HL；尾柄長13.1% SL；尾柄高6.9–7.2% SL；胸鰭長32.7–35.9% SL；腹鰭長9.6–12.4% SL．

特　徴　体は細長く，側扁する．頭は大きく，両眼間隔域は扁平．目は大きく，眼窩径は吻長にほぼ等しい．口は大きく，突出しない．上顎後端は眼の中央下に達する．下顎の先端は上顎の先端をわずかに超える．上顎前端に1対の大きな牙状歯があり，両顎には犬歯状歯が並ぶ．鋤骨と口蓋骨には微少な歯が存在する．鼻孔は2対．4–5本の鋸歯縁を有する鰓耙が第1鰓弓中央部と下肢にあり，上肢には小棘を帯びた瘤状の鰓耙が存在する．背鰭は2基で第1背鰭基底長は第2背鰭基底長の約2倍．臀鰭は第2背鰭とほぼ同形同大．胸鰭は長く，後端はほぼ臀鰭始部に達する．腹鰭は良く発達し，胸鰭始部下に位置する．側線は1本で背部外縁を平行に走り，第2背鰭後端下のわずか前方で終わる．鱗は円鱗で，脱落しやすく，形と大きさは不規則．体色は一様に暗褐色で，各鰭は黒褐色，口腔内は黒い．

分　布　中西部太平洋，インド洋，西部大西洋の温帯から熱帯域（Nakamura and Parin, 2001）．

備　考　本種は，以前はクロタチカマス科に含められる事もあったが，近年では独立した科として扱われることが多い（Nelson, 2006）．本種は，1科1属1種で構成され，クロタチカマス科とは眼窩径が吻長の1/2より大きいこと，胸鰭が長くほぼ臀鰭始部に達すること，側線が1本で背部外縁を平行に走ること等の特徴により識別できる．東部太平洋と南東部大西洋からの本種の採集記録はない（Nakamura and Parin, 2001）．本種の初期生活史に関する情報および科間の考察についてはPotthoff et al. (1980)に詳しく記載されている．

（日��）

 

 

Description  Body moderately elongate and compressed. Head large, with flat interorbital region. Eye large, its diameter almost as long as snout length. Mouth large, not protractile. Posterior margin of maxilla reaching below middle of eye. Lower jaw slightly projecting beyond upper jaw tip. Single pair of large fangs at front of upper jaw. A single row of strong canine teeth in both jaws. Several small teeth on vomer and palatine. Two nasal openings on each side of snout. Lower limb of first gill arch with 4–5 well-developed denticulate gill rakers, clusters of minute spines on upper limb, and a large denticulate gill raker at corner of first gill arch. Two dorsal fins. First dorsal-fin base about twice length of second dorsal-fin base. Anal fin similar to second dorsal-fin in size and shape. Pectoral fin very long, nearly reaching anal-fin origin. Pelvic fin well developed, originating below origin of pectoral fins. Caudal fin forked. Lateral line single, running close to dorsal contour, ending slightly before end of second dorsal fin. Scales cycloid, irregular in size and shape, highly deciduous. Body uniformly dark brown, fins blackish brown, oral cavity black.

Distribution  Tropical to temperate waters of Central and West Pacific, eastern Indian and western Atlantic oceans (Nakamura and Parin, 1993).

Remarks  This species was formerly put in the family Gempylidae, but is now classified in the monotypic family Scombrolabracidae (Nelson, 2006). It is distinguished from the family Gempylidae by the larger eye being a half of snout length, the greatly longer pectoral fin nearly reaching anal-fin origin, and a single lateral line running close to the dorsal contour. It has not been recorded from the eastern Pacific and southeastern Atlantic (Nakamura and Parin, 2001). The early life stages and familial relationships of this species were described in detail by Potthoff et al. (1980).

(K. Hidaka)