Abstract
A new species of the fish-parasitic isopod family Cymothoidae is described from the eastern Seto Inland Sea, western Japan. Nerocila domotoae sp. nov. is found from the caudal fins of silver croaker Pennahia argentata (Houttuyn, 1782) and Japanese whiting Sillago japonica Temminck and Schlegel, 1843. This new species is distinguished from all other species of Nerocila Leach, 1818 with serrate uropodal endopods by having the following traits: cephalon 0.8 times as long as wide, anterior margin rounded; antennule bases separated; antenna article 4 without dense cluster of setae on posterodistal margin; mandible palp article 3 with 1 long and 2–4 short terminal setae; maxilla with 2 recurved robust setae on medial lobe and 2 or 3 on lateral lobe; maxilliped palp article 3 with 3 recurved robust setae at tip and 1–3 on medial margin; pereopod 6 merus inferior margin with single robust seta in each of lateral and medial rows (i.e., 1 + 1), carpus inferior margin with 3 + 1 or 3 + 2 robust setae; pereopod 7 ischium inferior margin with single row of 1 or 2 robust setae, merus inferior margin with 2–4 + 3–5 (5–9 in total) robust setae, carpus inferior margin with 3–5 + 1–3 (5–7) robust setae; three light brown stripes on dorsal surface; pleotelson lateral margins convex, posterior margin converging to weak caudomedial point; uropodal endopod medial margin with notch, lateral margin with moderate to deep serration.