日本産魚類に寄生する等脚類に就いて

Abstract

Nine species of the Cymothoid Isopoda parasitic in the buccal or abdominal cavity of Japanese fishes are described in this report. They are Codonophilus trigonocephalus (Leach), Rhexanella verrucosa (Schi ?? dte & Meinert), Indusa minabensis n. sp., Cymothoa pulchra Lanchester, C. eremita Brünnich, Livoneca sacciger Richardson, L. samariscii u. sp., Irona melanosticta Schi ?? dte & Meinert, and Ichthyoxenus japonensis Richardson, and are parasitic in due order on Caranx (Longirostrum) delicatissimus (Döderlein), Pagrosomus major(Temminck & Schlegel), Chaunax fimbriatus (Hilgendorf), Diodon holacanthus Linné, Aulopus japonicus (Günther), Synaphobranchus pinnatus (Gronow), Samariscus japonicus Kamohara, Hyporhamphus sajori (Temminck & Schlegel), and Acheilognathus sp. All of them except Ichthyoxenus japonensis, which lives in the abdominal cavity, are discovered from the buccal or branchial cavity of the host. Cymothoa pulchra is recorded for the first time from Japan. The two new species are defined as follows: Indusa minabensis n. sp.: Female 23mm×13mm, nearly symmetrical and highly convex above. Head triangular, with distinct eyes. Antennae comparatively long and slender; those of the lst pair contiguous at the base, 8-jointed, and the 2nd pair longer being composed of 11-12 joints. Thorax oval in outline; antero-lateral angle of the lst segment not produced, but angular. Lateral parts of all thoracic segments slightly expanded having round post-lateral angle. Epimerae in the 2nd to 7th segments, narrow and linear. Basis of pereiopoda without carina. Abdomen one third as long as body; anterior segments covered by the 7th thoracic segment in lateral regions. Pleotelson more or less circular. Peduncle of uropod somewhat acuminate at inner distal angle; exopodite longer than endopodite. Male 10.5mm×5.0mm, relatively narrower than the female, symmetrical and slightly convex above. Head triangular, with distinct eyes. Both pairs of antennae comparatively longer than in the female, but composed of the same number of joints. Thorax oblong, with narrow epimerae. The lst abdominal segment not covered by the thorax. Pleotelson with margin round but more or less notched. Livoneca samariscii n. sp.: Represented only by a female. 10.1mm×5.9mm. Body only slightly convex above, asymmetrical having one side more expanded than the other, and with mar-supium vaulted but empty. Head triangular, very little immersed in the thorax, and with dis-tinct eyes. Antennae slender and long; those of the lst pair separated at the base, 8-jointed; the 2nd pair longer and 10-jointed. The lst thoracic segment sinuated in front, having anteriorly curved lateral parts and with angular antero-lateral corner. Other segments directed more or less obliquely backwards in lateral region and with anteriorly arched posterior borders. Epi-merae very narrow, linear, and shorter than lateral margins of segments. Pereiopoda without ca-rina on the basis. Abdomen nearly one third as long as body. The first 5 segments curved anteri-orly; lateral parts of anterior segments covered by the thorax on one side. Pleotelson semicircu-lar, two thirds as long as wide. Basis of uropod angular at inner distal corner; exopodite longer than endopodite. Lamellar maxilliped has anterior margin bearing a few short plumose setae and a palp tipped by 2 hooks.