ヨロイザメ科　Dalatiidae                  Kitefin Sharks

 

5 ヨロイザメ　　Kitefin Shark

Dalatias licha (Bonnaterre, 1788)

 

Specimen examined: 1 (SNFR 15933; 853 mm TL; 668 mm body length, BDL), 570–649 m depth.

Measurements: (% BDL=% body length, tip of snout to origin of upper lobe of caudal fin): total length 127.7; snout–vent length 80.8; head length 30.0; pre-dorsal-fin length 44.9; pre-second dorsal-fin length 81.6; first dorsal-fin anterior margin 11.5; length of first dorsal-fin base 7.2; second dorsal-fin anterior margin 11.5; length of second dorsal-fin base 8.7; dorsal margin of caudal fin 29.9; pectoral-fin anterior margin 17.2; length of pectoral-fin base 6.6; interdorsal space 33.2; eye length 3.7; eye height 2.2; prenarial length 3.4; preoral length 7.0.

 

計測形質：（％BDL）：全長 127.7；総排泄孔前長80.8；頭長 30.0；第1背鰭前長44.9；第2背鰭前長 81.6；第1背鰭前縁長 11.5；第1背鰭基底長 7.2；第2背鰭前縁長 11.5；第2背鰭基底長 8.7；尾鰭上葉長29.9；胸鰭前縁長 17.2；胸鰭基底長 6.6；背鰭間隔 33.2；眼径 3.7；眼高 2.2；鼻前長 3.4；口前長 7.0．

特　徴　吻は短く丸い．吻長は口幅より短く，頭長の約1/5．前鼻弁は短く，触鬚状にならない．鰓孔はやや大きく，鼻前長とほぼ等しい．口唇は肥厚するが吸盤状ではない．上顎歯と下顎歯は形が大きく異なり，上顎歯は小さく針状で湾曲し側尖頭はない．下顎歯は大きな三角尖で縁辺は鋸歯状．上顎の歯列は18列，下顎は19列．背鰭に棘はない．第1背鰭始部は胸鰭後端直上より後方，基底後端は腹鰭始部よりも前方．第2背鰭始部は腹鰭基底中央のほぼ直上．第2背鰭は第1背鰭よりやや大きいが，基底長は第1背鰭基底長の1.3倍以下．臀鰭はない．胸鰭は短く幅広で後端は丸い．尾鰭は非対称で，櫂状ではない．尾鰭上葉は長く，下葉は短い．尾鰭上葉の欠刻はよく発達する．尾柄部に尾柄欠刻，尾柄隆起はない．楯鱗は低く平らで単尖頭．体色は黒または黒褐色．

分　布 西部北大西洋：ジョージバンク，メキシコ湾北部．東部大西洋：北海，スコットランド，セネガル，モロッコ，西地中海，マデイラ，アゾレス諸島，アイルランド，コートジボワール，カメルーン．西インド洋：南アフリカ，南モザンビーク．西太平洋：日本，オーストラリア（南クイーンズランド州，グレートオーストラリア湾，南西オーストラリア），ニュージーランド．中部太平洋：ハワイ諸島 (Compagno, 1984)．

備　考　本種はヨロイザメ科の1属1種であり，ヨロイザメ科の他の種と，第1背鰭は体の中央背面付近にある，第１および第2背鰭の基底長はほぼ同じ長さ，第1背鰭前縁に棘はない等の形質より区別できる（波戸岡ほか, 2013）．

（青沼）

 

Description  Snout rounded, short, length much less than mouth width and about 1/5 of head length. Anterior nasal flap short, not expanded into barbel. Gill openings moderately broad and about equal to prenarial length. Lips very thick, not suctorial. Teeth very different in upper and lower jaws; upper teeth small, with narrow, hooked, needle-shaped cusps and no cusplets; lower teeth very large, bladelike, interlocked, with broad, erect, triangular cusps, small distal blades, and serrated edges; tooth rows 18/19. Both dorsal fins without spines. First dorsal-fin origin behind free rear tip of pectoral fin, first dorsal-fin insertion well anterior to pelvic-fin origin. Second dorsal-fin origin about over middle of pelvic-fin base. Second dorsal fin only slightly larger than first, its base less than 1.3 times first dorsal-fin base. Anal fin absent. Pectoral fin with short, broadly rounded free rear tips. Caudal fin asymmetrical, not paddle-shaped, upper lobe long, lower lobe very short, subterminal notch well developed. No pre-caudal pits and lateral keels on caudal peduncle. Dermal denticles with low flat, ridged, unicuspid crowns, not pedicellate. Color black or blackish brown.

Distribution  Western North Atlantic: Georges Bank, northern Gulf of Mexico. Eastern Atlantic: North Sea, Scotland, and Irish Atlantic Slope to Morocco, western Mediterranean, Madeira, Azores, West Sahara to Senegal, Ivory Coast to Cameroon. Western Indian Ocean: South Africa, southern Mozambique. Western Pacific: Japan, Australia (southern Queensland, Great Australian Bight, South West Australia), New Zealand. Central Pacific: Hawaiian Islands (Compagno, 1984).

Remarks  This species is the only member of the genus Dalatias. It is distinguished from other members of the family Dalatiidae by the following combination of characters: first dorsal fin located at about mid-point of body, length of both dorsal-fin bases almost equal, and anterior margin of first dorsal fin without spines (Hatooka et al., 2013).