カクレウオ科　Carapidae                                                         Pearlfishes

 

9 ミナミオニカクレウオ（新称）

Pyramodon punctatus (Regan, 1914)            Dogtooth pearlfish

 

Specimens examined: 2 (SNFR 16606, 16607; 60.5–68.1 mm HL, 342–350+ mm TL), 359–495 m depth (mid-water trawl).

Counts: D (to anal-fin origin, DRAO) 6–8, (to 31st vertebra, D₃₀) 49–51; A (to 31st vertebra, A₃₀) 50; P₁ 28; P₂ 2; developed GR 3; AV 16–17, (to dorsal fin origin, VDO) 6, (to anal fin origin, VAO) 9. Measurements (all expressed as % HL): body depth at anal-fin origin 78.4–90.4; snout length 20.2–21.1; orbit diameter 20.0–20.7; interorbital width 21.0–22.3; upper-jaw length 51.4–51.6; lower-jaw length 55.9–56.4; pectoral-fin length 74.0–80.8; pelvic-fin length 26.6–27.9; predorsal-fin length 119.8–121.7; distance from snout to anus 132.2–139.5; prepelvic-fin length 71.8–74.7.

 

計数形質：背鰭（臀鰭始部直上まで）6–8軟条，（第31椎体前端直上まで）49–51；臀鰭（第31椎体前端直下まで）50；胸鰭28軟条；腹鰭2軟条；棒状の鰓耙数 3；腹椎骨数16–17，（背鰭始部下まで, VDO）6，（臀鰭始部上まで，VAO）9．計測形質：（全て% HL）　体高（臀鰭始部上）78.4–90.4；吻長 20.2–21.1；眼窩径 20.0–20.7；両眼間隔幅 21.0–22.3；上顎長 51.4–51.6；下顎長 55.9–56.4；胸鰭長74.0–80.8；腹鰭長 26.6–27.9；背鰭前長 119.8–121.7；吻端から肛門までの距離 132.2–139.5；腹鰭前長71.8–74.7．

特　徴　体は細長く，側扁し，尾部はヒモ状．吻は尖り，眼と口はやや大きい．両顎先端に１対の犬歯がある．上顎に，犬歯状の1内列歯と小円錐歯からなる歯帯をもつ．下顎に犬歯状歯6–7本が疎らに並ぶ．鋤骨に1犬歯と小犬歯状歯からなる歯帯をもつ．口蓋骨に不規則な1–2列の犬歯状歯が並ぶ．背鰭と臀鰭は各1基．背鰭始部は胸鰭基底より後方，臀鰭始部より前方，腹鰭は峡部に近い．肛門は臀鰭始部の直前．体は小円鱗で覆われる．頭部と鰭は頬部を除き黒色から黒褐色．体側はやや白く，小黒点が散在する．腹部は褐色で青味を帯びる．背鰭と臀鰭の，後部1/4は黒色．

分　布　インド・西太平洋の南半球の熱帯から温帯水域．近底生性で，採集水深は120–731 m（Nielsen et al., 1999）．

備　考　オニカクレウオ属には自由生活をする4種が知られ，本種は次の形質の組合わせにより同属他種と識別できる：胸鰭鰭条数が26–28（vs. バケオニカクレウオP. lindas Markle and Olney, 1999では21–25，オニカクレウオP. ventralis Smith and Radcliffe, 1913では24–26），第31脊椎骨までの臀鰭条数 (A₃₀) が47–51（vs. P. parini Markle and Olney, 1999では43–47）腹椎骨数が17–19（vs. P. ventralis では14–15，P. pariniでは15–16），背鰭と臀鰭の，後部1/4が黒色（vs. P. lindasでは縁辺がすべて黒色，P. pariniでは黒色部がない）(Markle and Olney, 1990; Nielsen et al., 1999)．調査した1標本（SNFR 16606）の腹椎骨数は16で既知の変異幅より少ないが，その他の特徴は本種のものによく一致した．

（遠藤）

 

Description  Body elongated, compressed, with long tapering tail. Snout moderately sharp. Eye rather large. Mouth large, terminal. A pair of strong canines on symphysis of each jaw, slightly separated from second tooth; larger on lower jaw. On upper jaw, a tooth band comprising an inner row of enlarged canine-like teeth and outer minute teeth. On lower jaw, one row of 6–7 small to moderate canine-like teeth sparsely arrayed. On vomer, a strong, large canine followed by a small patch of smaller canine-like teeth posteriorly. On palatine 1–2 irregular rows of canine-like teeth. Single dorsal and anal fins with long bases. Dorsal-fin origin located behind pectoral-fin insertion, before anal-fin origin. Pelvic fin close to isthmus. Anus just before anal-fin origin. Body fully covered with small cycloid scales. Head and fins black to dark brown except cheek pale. Body whitish laterally with many minute black spots. Abdomen dark brown, somewhat bluish. Posterior quarter of vertical fins blackish.

Distribution  Indo-West Pacific of the southern hemisphere from tropical to temperate waters. Benthopelagic in 120–731 m (Nielsen et al., 1999).

Remarks  Pyramodon is composed of four free-living species (Nielsen et al., 1999), and the present species can be distinguished from its congeners by the following combination of characters: 26–28 pectoral-fin rays (vs. 21–25 in P. lindas Markle and Olney, 1999; 24–26 in P. ventralis Smith and Radcliffe, 1913); 47–51 anal-fin rays to 31st vertebra, A₃₀ (vs. 43–47 in P. parini Markle and Olney, 1990); 17–19 abdominal vertebrae (vs. 14–15 in P. ventralis, 15–16 in P. parini); and blackish pigmentation on posterior quarter of vertical fins (vs. whole margins blackish in P. lindas; blackish area absent in P. parini) (Markle and Olney, 1990; Nielsen et al., 1999). The specimen of SNFR 16606 has 16 abdominal vertebrae, which is fewer than the previously known range of 17–19, but the other characters of this specimen agree well with those of P. punctatus.