クロタチカマス科　Gempylidae            Snake Mackerels

37 クロシビカマス
Promethichthys prometheus (Cuvier, 1832)     Roudi Escolar

Specimens examined: 10 (SNFR 16056–16065; 488–625 mm SL), 360–385 m depth.

Counts: D XVII–XIX-II, 15–18+2; A II, 13–16+2; P₁ 13–14; P₂ I; GR 5–10+8–16=13–24; LLS 131–144; V 20+14=34. Measurements: head length 27.5–30.0% SL; body depth 13.6–15.7% SL; eye diameter 23.9–27.2% HL; snout length 38.6–40.2% HL; interorbital width 21.2–25.1% HL; upper-jaw length 46.5–49.3% HL; lower-jaw length 61.4–67.0% HL; caudal-peduncle length 5.6–7.8% SL; caudal-peduncle depth 4.3–5.0% SL; longest pectoral-fin ray length 15.5–17.8% SL.

計数形質：背鰭17–19棘-2棘，15–18軟条+2（小離鰭）；臀鰭2棘，13–16軟条+2（小離鰭）；胸鰭13–14軟条；腹鰭1棘；鰓耙数5–10+8–16=13–24；側線鱗数131–144；脊椎骨数20+14=34．計測形質：頭長27.5–30.0% SL；体高13.6–15.7% SL；眼径23.9–27.2% HL；吻長38.6–40.2% HL；両眼間隔21.2–25.1% HL；上顎長46.5–49.3% HL；下顎長61.4–67.0% HL；尾柄長5.6–7.8% SL；尾柄高4.3–5.0% SL；胸鰭最長軟条長15.5–17.8% SL．

特　徴　体は細長く，側扁する．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．上顎後端は瞳孔前縁下に達する．下顎の先端は上顎の先端をわずかに超える．上顎前端に2–3対の大きな牙状歯がある．両顎には1列の犬歯状歯が並ぶ．鋤骨に歯は無く，口蓋骨には微少な歯が存在する．鼻孔は2対．鰓耙は隅角部のやや大きな1本を除き小棘状．第1背鰭は第2背鰭とほぼ同高で，第1背鰭基底長は第2背鰭基底長の約2.5倍．臀鰭は第2背鰭とほぼ同形同大．背鰭および臀鰭の後方に，それぞれ2個の小離鰭がある．胸鰭はやや小さく，先端は截形．腹鰭は退縮し皮下に埋没する．側線は1本で前部では背縁近くを通り，背鰭第4棘から6棘の下方にかけて急に下降し，それ以降は緩やかに下降して尾柄部では体側中央のわずか下方を走る．頭と体に微少な円鱗があり，脱落しやすい．体および各鰭は黒褐色，口腔内は黒い．

分　布　太平洋，インド洋，大西洋の温帯から熱帯域 (Nakamura and Parin, 1993)．

備　考　本種は，1属1種で構成され，分離した臀鰭棘を持たないこと，急下降する側線を持つこと等の特徴により本科他属から識別できる．また本種は全世界の温帯から熱帯域に分布するが，東部太平洋域ではサラ・イ・ゴメス海嶺からのみ報告されている（Nakamura and Parin, 1993）．

（日��）

Description  Body moderately elongate and compressed. Head large, with slightly concave interorbital region. Mouth large, not protractile when opened. Posterior margin of maxilla reaching to anterior margin of pupil. Lower jaw ending slightly anterior to upper jaw. Two or three pairs of large fangs at front of upper jaw. A single row of canine teeth in both jaws. No teeth on vomer and several small teeth on palatine. Two nostrils on each side of snout. Gill rakers minute except long one at corner of first gill arch. First and second dorsal fins subequal in height. First dorsal-fin base 2.5 times second dorsal-fin base. Anal fin similar to second dorsal fin in shape and size. Two finlets present posterior to both dorsal and anal fin. Pectoral fin short, with truncated end. Pelvic-fin spine mostly buried in skin. A single lateral line running subdorsally from above upper angle of gill opening to under fourth spine of first dorsal fin, then abruptly curving down below between fourth and sixth spines of first dorsal fin, thereafter gradually descending, and running straight along mid-caudal peduncle. Scales on body and head, small, cycloid, very deciduous. Body and fins uniformly blackish brown, oral cavity black.

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

Remarks Promethichthys is monotypic and can be distinguished from the other gempylid genera by having no free anal-fin spines and the lateral line curving abruptly downward below about the fourth and sixth dorsal-fin spines. Promethichthys prometheus is distributed in the tropical and warm temperate waters of all oceans, but appears to be absent from the eastern Pacific except for the Sala y Gomez Ridge (Nakamura and Parin, 1993).

(K. Hidaka)