エボシダイ科　Nomeidae                                     Driftfishes

 

43 ハナスベオキメダイ（新称）

Cubiceps capensis (Smith, 1845)                   Cape Fathead

 

Specimens examined: 4 (SNFR 16443, 16444, 16590, 16591; 363–390 mm SL), 117–458 m depth.

Counts: D XI-I, 21–22; A III, 20–21; P₁ 22–23; P₂ I, 5; GR 9+19–20=28–29; LLS 62–64; V 12+19=31; upper procurrent caudal-fin rays 10–11; lower procurrent caudal-fin rays 8–11. Measurements: head length 28.9–30.0% SL; body depth 27.6–29.9% SL; pre-dorsal fin length 31.1–39.6% SL; pre-anus length 56.6–59.6% SL; pectoral-fin length 36.8–41.1% SL; pelvic-fin length 12.2–13.1% SL; caudal-peduncle length 10.8–11.6% SL; caudal-peduncle depth 9.3–10.2% SL; eye diameter 24.0–27.2% HL; interorbital width 29.6–33.1% HL; snout length 29.1–31.5% HL; upper-jaw length 33.3–35.1% HL; lower-jaw length 34.6–36.8% HL.

 

計数形質：背鰭11棘-1棘，21–22 軟条；臀鰭3棘，20–21軟条；胸鰭22–23軟条；腹鰭1棘，5軟条；鰓耙数9+19–20=28–29；側線鱗数 62–64；脊椎骨数12+19=31；尾鰭上葉の前起鰭条10–11；尾鰭下葉の前起鰭条8–11．計測形質：頭長28.9–30.0% SL；体高27.6–29.9% SL；背鰭前長31.1–39.6% SL；肛門前長56.6–59.6% SL；胸鰭長36.8–41.1% SL；腹鰭長12.2–13.1% SL；尾柄長10.8–11.6% SL；尾柄高9.3–10.2% SL；眼径24.0–27.2% HL；両眼間隔29.6–33.1% HL；吻長29.1–31.5% HL；上顎長33.3–35.1% HL；下顎長34.6–36.8% HL．

特　徴　体は長楕円形で側扁し，尾柄部は短くて低い．吻は丸く，吻長は眼径よりも長い．両顎，鋤骨，口蓋骨，および舌上には微少な円錐歯が1列に並ぶ．眼は楕円形で大きい．涙骨は上顎のほとんどを被う．主鰓蓋骨は薄く，強い棘はない．背鰭始部は胸鰭基部の直上付近に位置する．第2背鰭と臀鰭の基底はともに長い．臀鰭の3棘は短くて硬い．胸鰭は極めて長く，その長さは頭長よりも長い．腹鰭は短く，基部は胸鰭基部よりもわずかに後方に位置する．尾鰭は深く二叉する．肛門は第2背鰭始部の直下付近に位置する．鱗は薄い円鱗で，剥がれやすく，頭頂部や峡部にも存在するが，吻端から眼の前縁までの領域は無鱗．食道嚢をもつ．体はほぼ一様に茶褐色で，口内は黒い．

分　布　世界中の亜熱帯域（Parin and Piotrovsky, 2004）．

備　考　本種は，オキメダイC. baxteri McCulloch, 1923に最もよく似るが，吻端から眼の前縁までの領域が無鱗であること（オキメダイには鱗がある）によって識別できる．Butler (1979)による本属種の分類学的研究において，本種の尾鰭上葉の前起鰭条（upper procurrent rays）の数はオキメダイとの重要な識別形質とされたが，実際は範囲が重複しており，識別形質にはならない（Agafonova, 1994）．インド洋南西部には同属のミナミオキメダイC. caeruleus Regan, 1914，ホソオキメダイC. pauciradiatus Günther, 1872，ボウズコンニャクC. whiteleggii (Waite, 1894)が分布するが，本種は鋤骨歯が1列であること（他種では歯帯を形成する），同様に舌上にも1歯列をもつこと（他種はもたない）によって異なる．

（岡本）

 

Description  Body long, oval, compressed; caudal peduncle short and shallow. Snout round, its length longer than eye diameter. A single row of minute conical teeth present on both jaws, vomer, palatine and tongue. Eye elliptical, large. Lachrymal bone almost completely covering upper jaw. Operculum thin, without spines. Dorsal-fin origin above pectoral-fin base. Bases of second dorsal and anal fins long. Three anal-fin spines, short and stiff. Pectoral fin extremely long, its length longer than head. Pelvic fin short, its base slightly posterior to pectoral-fin base. Caudal fin deeply forked. Anus located just below origin of second dorsal fin. Scales cycloid, thin and deciduous, extending to upper part of head region and isthmus; snout tip to anterior margin of eye naked. Pharyngeal sac present. Body uniformly dark brown, oral cavity black.

Distribution  Subtropical waters of the world’s oceans (Parin and Piotrovsky, 2004).

Remarks  This species is most similar to C. baxteri McCulloch, 1923, but can be distinguished by the naked region from the snout tip to the anterior margin of eye (vs. snout totally scaled in C. baxteri). Butler (1979) stated in a taxonomic revision of this genus that these two species were distinguished by the number of upper procurrent caudal-fin rays, but Agafonova (1979) reported an overlap of this character between the two species. Three other species of the genus, C. caeruleus Regan, 1914, C. pauciradiatus Günther, 1872, and C. whiteleggii (Waite, 1894) are distributed in the western South Indian Ocean. C. capensis differs from these congeners by having a single row of teeth on the vomer (vs. a tooth patch) and tongue (vs. toothless).

(M. Okamoto)