Redescription of Sandythoa samariscii (Shiino, 1951), a fish parasitic isopod (Cymothoidae), with a new host record

Abstract Sandythoa samariscii (Shiino, 1951), a branchial fish parasite, originally described as Livoneca samariscii Shiino, 1951, was based on a single female specimen collected from Kochi Prefecture, Japan. Since the original description, no additional specimens have been recorded, and the type material is currently presumed to be missing, precluding a definitive taxonomic reassessment. In the present study, we redescribe an adult female of S. samariscii based on a newly collected specimen from the cynoglossid tongue sole Symphurus sp. off Amami-Oshima Island, Japan. An associated male specimen was also collected for the first time, and its morphology is described herein; new host and locality records are provided. Specimens were identified as S. samariscii based in concordance with diagnostic characters outlined in the original description. In addition, several newly recognised diagnostic features are presented: slight constriction at the bases of antennula article 8 and antenna article 10; bases of pereopods 1-3 broader than those of pereopods 4-7; and the presence of numerous plumose setae along the maxilliped margins. The male of S. samariscii differs from those of other Sandythoa species in the following features: asymmetrical body, slightly twisted to one side; antenna with 11 articles, the terminal article slightly constricted basally; mesial margins of pleopod 4-5 exopods concave; pleopods 2-5 each bearing 4-5 coupling hooks; and pereopods 1-7 with robust setae.