オンデンザメ科　Somniosidae          Sleeper Sharks

 

4 マルバラユメザメ　Portuguese Dogfish

Centroscymnus coelolepis Barbosa du Bocage and de Brito Capello, 1864

 

Specimen examined: 1 (SNFR 16714; 954 mm TL; 753 mm body length, BDL), 618–698 m depth.

Measurements: (% BDL=% body length, tip of snout to origin of upper lobe of caudal fin): total length 126.7; snout–vent length 81.5; head length 26.8; pre-dorsal-fin length 46.6; pre-second dorsal-fin length 88.8; first dorsal-fin anterior margin 10.2; length of first dorsal-fin base 7.3; second dorsal-fin anterior margin 11.5; length of second dorsal-fin base 9.0; dorsal margin of caudal fin 27.4; pectoral-fin anterior margin 18.9; length of pectoral-fin base 6.5; interdorsal space 35.5; eye length 4.2; eye height 2.4; prenarial length 2.1; preoral length 8.6.

 

計測形質：（％BDL）：全長 126.7；総排泄孔前長81.5；頭長 26.8；第1背鰭前長46.6；第2背鰭前長 88.8；第1背鰭前縁長 10.2；第1背鰭基底長 7.3；第2背鰭前縁長 11.5；第2背鰭基底長 9.0；尾鰭上葉長27.4；胸鰭前縁長 18.9；胸鰭基底長 6.5；背鰭間隔 35.5；眼径 4.2；眼高 2.4；鼻前長 2.1；口前長 8.6．

特　徴　体はずんぐりし，胸部域から後方に急に先細りしない．吻は短く，頭長の1/4未満，口前長は眼の後端から第1鰓孔までの長さよりやや短く，口幅よりも短い．口唇は肉厚．上唇褶は非常に短い．下顎歯は，非常に短く側方に強く傾く尖頭を備え，その基部は狭く高い．第1背鰭と第2背鰭はほぼ同大で，背鰭棘は短いが先端は鰭より突出する．第1背鰭始部は胸鰭より後方で基底は前方に伸長しない．第2背鰭基底長は両背鰭間隔および第2背鰭基底後端から尾鰭上葉始部の間隔より短い．第2背鰭後端は尾鰭上葉始部に達しない．臀鰭はない．胸鰭はやや大きく，胸鰭前縁長は第１背鰭前縁長の約2倍．腹鰭後端は第2背鰭始部より後方に伸長する．体側鱗は大きく，縁はなめらかで円形．色は黒褐色．

分　布 北西大西洋：グランドバンクスからデラウェア湾．東部大西洋：アイスランドから大西洋斜面に沿って南セネガル，アゾレス諸島，マデイラ島，ギニア，シエラレオネまで，ナミビア南部から南アフリカの喜望峰西岸まで．地中海西部．西部太平洋：南シナ海，日本，ニュージーランド．インド洋南西部（Compagno, 1984; 波戸岡ほか, 2013）．

備　考 本種はユメザメCentroscymnus owstonii Garman, 1906とよく似るが，吻は短い，第1・第2背鰭はほぼ同大，躯幹部腹側縁辺に隆起線はない，背部の体側鱗は大きい等の特徴よりユメザメと区別される（波戸岡ほか, 2013）．

（青沼）

 

Description  Body stocky, not strongly tapering posterior to pectoral region. Snout short, less than 1/4 of head length. Preoral length slightly less than distance from posterior end of eye to first gill slit and less than mouth width. Lips not thick and fleshy. Upper labial furrows very short. Lower teeth with very short, strongly oblique cusps and high. Dorsal fins about equal in size and height, fin spines very small but with tips protruding from fins. First dorsal-fin base not extending forward as a prominent ridge, origin behind pectoral fin; second dorsal-fin base shorter than distance between its insertion and upper caudal-fin origin, and between two dorsal fins. Anal fin absent. Free rear tip of second dorsal fin well anterior to upper caudal origin. Pectoral fin moderately large, length of anterior margin about twice first dorsal-fin anterior margin. Free rear tips of pelvic fins extending beyond second dorsal-fin insertion. Lateral trunk denticles very large, with smooth, circular, ridgeless and acuspidate crowns. Color blackish brown.

Distribution  Western North Atlantic: Grand Banks to Delaware Bay. Eastern Atlantic: Iceland south along Atlantic slope to Senegal, Azores, Madeira, Guinea to Sierra Leone, and southern Namibia to the south-western Cape coast of South Africa; also western Mediterranean. Western Pacific: South China Sea, Japan, New Zealand. Western South Indian Ocean (Compagno, 1984; Hatooka et al., 2013).

Remarks  This species is close to C. owstonii Garman, 1906, but it is distinguished by the following characters: snout short, both dorsal fins almost equal in size, flank without ridge, and dorsal denticles large (Hatooka et al., 2013).