相模湾および駿河湾で得られたフトツノザメ Squalus mitsukurii （ツノザメ目ツノザメ科）の成長に伴う形態変化について
2019 年 2019 巻 40 号 p. 59-65
詳細
2019 年 2019 巻 40 号 p. 59-65
Morphological changes accompanying the growth of the shortspine spurdog, Squalus mitsukurii (Squaliformes: Squalidae) were examined in ten specimens of 304.1 to 952.6 mm in total length (TL), collected from Sagami and Suruga bays, Japan. The caudal fin of specimens less than 330 mm TL has a broad white margin on the upper lobe, and the lower lobe is overall white. The upper lobe changes from having a rounded tip to a pointed tip at total lengths between about 450 to 500 mm, and the white posterior margin of the caudal fin also narrows in specimens of this size. The dermal denticles on the anterior part of the first dorsal fin in smaller specimen are arranged with a space between each one, bearing a tricuspid leaf-like portion and a stalk at the base. On the other hand, the dermal denticles change to a rhomboidal shape and become arranged in a muriform pattern without spaces between them in larger specimens. In comparison with Squalus sp. 2 specimens less than 324.1 mm TL, it is suggested that S. mitsukurii specimens of the same size are distinguished in having the second dorsal spine less covered with dermal denticles.
