ミシマオコゼ科　Uranoscopidae                          Stargazers

35 ムカシミシマ

Pleuroscopus pseudodorsalis Barnard, 1927 Scaly Stargazer

Specimens examined: 8 (SNFR 19247–19252, 19266, 19267; 261–307 mm SL), 572–988 m depth.

Counts: D VIII–XI-9–11; A 10–12; P₁ 23–25; GR 4–5+19–20=23–26. Measurements: head length 32.8–36.3% SL; body depth 16.6–21.8% SL; body width 29.3–35.7% SL; orbit diameter 22.9–25.4% HL; interorbital width 35.0–51.6% HL; snout length 27.1–30.9% HL; upper-jaw length 51.9–62.1% HL; caudal-peduncle length 10.4–12.3% SL; caudal-peduncle depth 8.2–11.1% SL; pectoral-fin length 24.6–26.6% SL; pelvic-fin length 17.8–20.2% SL; caudal-fin length 21.7–23.5% SL.

計数形質：背鰭8–11棘-9–11軟条；臀鰭10–12軟条；胸鰭23–25軟条；鰓耙数4–5+19–20=23–26．

計測形質：頭長32.8–36.3% SL；体高16.6–21.8% SL；体幅29.3–35.7% SL；眼径22.9–25.4% HL；両眼間隔35.0–51.6% HL；吻長27.1–30.9% HL；上顎長51.9–62.1% HL；尾柄長10.4–12.3% SL；尾柄高8.2–11.1% SL；胸鰭長24.6–26.6% SL；腹鰭長17.8–20.2% SL；尾鰭長21.7–23.5% SL．

特　徴　体は太く，頭が大きい．頭部背面は扁平．体は前部で縦扁し，後部でやや側扁する．頭の側面と背面は骨質隆起をともなう硬い骨板で被われる．小型個体（253 mm SL）では眼窩上方が上向きに突出するが，この突出部は成長にともなって退縮する．小型個体では後頭部背面にも骨質の突出部が一対あるが，大型個体では退縮する．体は硬い鱗で被われる．腹部の鱗は成長にともない失われる．鱗は円鱗で，小型個体では鱗の表面に3–5本の顆粒突起列をともなうが，大型個体では鱗表面の突起が不明瞭になる．眼は頭の側面につき，口は上位．背鰭棘条は8–11本の短く不動の骨質突起で，鰭膜を欠く．臀鰭基底は短く，背鰭軟条部と同程度．尾鰭後縁はやや丸い．腹鰭は互いに近接し，喉部に位置する．側線は体側中央を走り，尾鰭上に伸びる．頭と体は暗灰色で腹面は白い．小型個体では側面と背面に多数の小さな黒色斑があるが，大型個体では不定形の模様になる．

分　布　南半球の温帯から亜熱帯にあたる南アフリカ，マダガスカル，オーストラリア南部およびニュージーランド沖（Kishimoto et al., 1988）．

備　考　Pleuroscopusには本種のみが知られる．本属は，背鰭棘条が鰭膜で連続せず8–11個の退化的な突起状であること，背鰭軟条部および臀鰭の基底が短いこと，鱗の表面に顆粒突起列があることなど固有の特徴により，同科他種と容易に識別される．本種は成長にともなって形態や色彩が大きく変化する（Kishimoto et al., 1988）．

（松沼）

Description  Head and body broad. Head flattened dorsally. Body depressed anteriorly, slightly compressed posteriorly. Lateral and dorsal surfaces of head encased in sculptured bones. Supraocular portion expanded dorsally to form a ridge in a small specimen of 253 mm SL, but ridge reduced with growth. Paired bony ridges present posterodorsally on head in small specimens, but reduced in larger specimens. Body covered with strong scales, progressively lost from belly in larger specimens. Scales cycloid, with 3–5 granular ridges on exposed surface in small specimens, but ridges reduced in large adults. Eye lateral. Mouth superior. Dorsal-fin spines unconnected, reduced to 8–11 short immovable bony tubercles anterior to soft-rayed portion of dorsal fin. Anal-fin base short, its length subequal to that of dorsal fin. Caudal fin slightly rounded. Pelvic fins close together, on isthmus. Lateral line midlateral, extending on to caudal fin. Head and body dark gray, whitish ventrally; numerous small dark blotches scattered dorsally and laterally in small specimens; undefined dark markings in large specimens.

Distribution  Subtropical to temperate waters of the Southern Hemisphere off South Africa, Madagascar, southern Australia and New Zealand (Kishimoto et al., 1988).

Remarks  Pleuroscopus is monotypic and easily distinguished from all other members of the family in having unique characters including unconnected dorsal-fin spines that are reduced to short immovable tubercles, short soft-rayed portions of the dorsal and anal fins, and scales with granular ridges. This species shows dramatic ontogenetic changes in morphology and coloration (Kishimoto et al., 1988).

 (M. Matsunuma)