Gyrodactylus rasini Lucky, 1973 (Figures 1, 2, 3A, 4A ±C, 5, 9A, B) Synonymy: Gyrodactylus bullatarudis Turnbull, 1956 of Harris (1986). Voucher specimens: The Natural History Museum, London (BM(NH) 1994.11.24.13 ±18). Host: Xiphophorus helleri Ö X. maculatus hybrids imported into UK from ornamental ®sh farms in Singapore. Site: external surface, too few infected ®sh seen to give more details. A`very small’ species according to scheme of Harris (1985). Body length of moderately ¯attened, moderately contracted specimens, less than 400 m m. Anterior of the pharynx (see Kritsky, 1971) consisted of eight cells arranged in a ring which were fused to each other along their lateral borders. Thirty-seven ¯attened specimens mounted in ammonium picrate-glycerin for sclerite examination had a pharynx mean length of 41 m m (SD 5 m m) and width of 37 m m (SD 4 m m). The anterior and posterior pharyngea l bulbs were of approximatel y equal width, although the width of the posterior part was greater for most specimens. Measurements of attachment hooks and bars are given in table 1; ventral bars and marginal hooks were most distinctive (®gures 1 and 9). The ventral bar had long, slightly curved antero-lateral processes, converging towards each other apically (®gure 1). The dorsal bar had a median notch (®gure 1), though this was not always obvious. Marginal hook blade point was extended nearly level with or beyond the toe. The marginal hook blade had a pronounced bend immediately before the point (®gure 1), just visible using phase contrast, was most readily seen by SEM (®gure 2). The cirrus had one large spine with a bifurcate base at both sides (®gure 3A) and a single row of four to seven small spines (®gures 3A and 4).

Published as part of Richards, G. R., Veltkamp, C. J. & Chubb, J. C., 2000, Di erentiation of Gyrodactylus bullatarudis Turnbull, 1956 and G. rasini Lucky, 1973 (Monogenea) with reassignment of Gyrodactylus bullatarudis Turnbull, 1956 sensu Harris (1986) to G. rasini, pp. 341-353 in Journal of Natural History 34 (3) on page 344, DOI: 10.1080/002229300299525, http://zenodo.org/record/5279510