A new monogenean genus from an ephippid fish off Peninsular Malaysia.

Sundatrema langkawiense n. g., n. sp. (Monogenea: Ancyrocephalidae) is described from the gills of the orbfish Ephippus orbis (Bloch) (Ephippidae) off the Island of Langkawi, Malaysia, in the Andaman Sea. This new genus has the ancyrocephalid characteristics of four anchors, 14 marginal hooks and two bars, but differs from other four-anchored monogenean genera, and notably from Parancylodiscoides Caballero & Bravo Hollis, 1961 (found on the ephippids Chaetodipterus spp. off Central and South America), by having a unique combination of features. These include a muscular genital sucker and a vas deferens and vagina on the same (sinistral) side of the body. It is similar to Parancylodiscoides in having four haptoral reservoirs opening at the anchoral apertures, four anchors, similar connecting bars and small marginal hooks. The new species is characterised by the above generic features and by possessing a small, short copulatory organ lacking an accessory piece. Diplectanum longiphallus MacCallum, 1915 (previously attributed to Ancyrocephalus Creplin, 1839, Tetrancistrum Goto & Kikuchi, 1917 and Pseudohaliotrema Yamaguti, 1953) is transferred to Parancylodiscoides as P. longiphallus (MacCallum, 1915) n. comb.