アジ科 Carangidae Jacks
28 ムロガタマアジ（新称）
Trachurus longimanus
(
Specimens
examined: 4 (SNFR 16586–16589; 307–309 mm SL), 117–132
m depth.
Counts:
D XIII-I, 33–36; A II-I, 29–30; P1 20–23;
P2 I, 5; GR 13–16+35–38=51–53; LLS 45–51 in curved part, 42–50 in
straight part, 87–100 in total; V 10+14=24. Measurements: head length 26.0–27.1%
SL; body depth 21.1–22.7% SL; eye diameter 23.2–24.4% HL; interorbital
width 18.7–21.7% HL; snout length 25.4–28.3% HL; upper-jaw length 35.9–39.6%
HL; lower-jaw length 45.1–48.8% HL; caudal-peduncle length 30.5–33.8% HL;
caudal-peduncle depth 12.5–13.7% HL; pectoral-fin length 101.6–110.4% HL;
pelvic-fin length 46.7–50.8% HL.
計数形質：背鰭8棘-1棘，33–36軟条；臀鰭2棘-1棘，29–30軟条；胸鰭20–23軟条；腹鰭1棘，5軟条；鰓耙数13–16+35–38=51–53；側線鱗数 湾曲部45–51，直走部42–50，合計87–100；脊椎骨数10 + 14 = 24．計測形質：頭長26.0–27.1%
SL；体高21.1–22.7%
SL；眼径23.2–24.4%
HL；両眼間隔18.7–21.7%
HL；吻長25.4–28.3%
HL；上顎長35.9–39.6%HL；下顎長45.1–48.8%
HL；尾柄長30.5–33.8%
HL；尾柄高12.5–13.7%
HL；胸鰭長101.6–110.4%
HL；腹鰭長46.7–50.8%
HL.
特 徴 体は紡錘形に近く，やや側扁する．吻は尖る．眼に脂瞼が発達する．歯は微小な円錐歯で，両顎，鋤骨，口蓋骨および舌上にある．背鰭は2基で，第1背鰭の方が高い．臀鰭の最初の2棘は鰭本体から離れる．背鰭および臀鰭の最終軟条は長く，鰭本体から離れるが，直前の軟条と低い鰭膜で連結する．胸鰭は長く鎌形．側線は前部で湾曲し，後部で直線状．背方側線分枝は後方に延びて第2背鰭の始部に達する．鱗は円鱗で剥がれやすい．側線鱗は上下に広く，幅は湾曲部では体長の2.7–2.9%，直走部では最大で体長の3.2–3.8%．側線湾曲部と直走部の鱗の上下幅の比率は1.19–1.39．側線鱗の後部40–52枚（および尾鰭上の数枚）は稜鱗．鰓蓋に1黒斑がある．尾鰭は赤みを帯びる．
分 布 南大西洋（トリスタンダクーニャ島，ベマ海嶺），インド洋南西部（マダガスカル島南方約700kmの海山Walters
Shoals，南西インド洋海嶺）（Collette and Parin, 1991; 本研究）．
備 考 本種の背鰭および臀鰭の最終軟条は，伸長して鰭本体から離れることでムロアジ属Decapterusの小離鰭に似るが，低い鰭膜で直前の軟条とつながることで異なる．本種はムロアジ属とは，背方側線分枝が後方に延びて第2背鰭始部に達する（ムロアジ属では後頭部に留まる）こと，側線湾曲部の鱗が上下に広い（体長の3.2–3.8%
vs. 2%未満）こと，鰓腔後縁に突起がない（vs.
突起が2個ある）ことで異なり，他のマアジ属魚類と一致する (Smith-Vaniz, 1999; 本研究)．本種は側線湾曲部の鱗が最後の0–3個を除き後縁に棘を欠き稜鱗ではない（他の本属魚類ではほとんどが稜鱗:
Berry and Cohen, 1974）ことで他の本属魚類と異なる．
(星野)
Description
Body
nearly fusiform but more or less compressed. Snout
pointed. Adipose eyelid developed. Teeth minute, conical, on both jaws, vomer, palatine and tongue. Two dorsal fins, first one
higher. First two anal-fin spines detached. Last soft ray of dorsal and anal
fins elongated and displaced, but connected to its preceding ray by a very low
membrane. Pectoral fin long, falcate. Lateral line arched anteriorly,
straight posteriorly. Dorsal accessory lateral line
extending posteriorly to second dorsal-fin origin.
Scales cycloid, deciduous. Lateral-line scales expanded dorsoventrally;
heights of scales in curved part 2.7–2.9% SL and those of largest scales in
straight part 3.2–3.8% SL; ratio of height of straight to curved lateral-line
scales 1.19–1.39; posterior 40–52 scales (and several of those on caudal fin)
forming scutes. A dark opercular
spot present. Caudal fin reddish.
Distribution South
Atlantic Ocean (Tristan da Cunha,
Vema Seamount), and western
Remarks The last ray of dorsal and anal fins of
this species resembles a finlet of Decapterus by its
elongated and detached appearance, but it is connected to the preceding ray by
a very low membrane. This species differs from Decapterus and agrees with
congeners in having a posteriorly elongated dorsal
accessory lateral line extending to the second dorsal-fin origin (vs. not
extended beyond occipital region in Decapterus), scales in curved part of lateral line expanded dorsoventrally (3.2–3.8% SL vs. less than 2% SL), and papillae
absent on posterior margin of gill chamber (two papillae present) (Smith-Vaniz, 1999; present study). This species differs from
congeners in lacking scutes in the curved part of
lateral line except the last 0–3 scales (vs. mostly scutes
in other members of Trachurus:
(K.
Hoshino)