Gyrodactylus rasini Lucky, 1973

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, Journal of Natural History 34 (3), pp. 341-353 : 344

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).

Figures

FIG. 1. Attachment hooks and bars of G. rasini from a Xiphophorus hybrid. Note the longer ventral bar processes and di€erent marginal hook sickle morphology in comparison to ®gure 6.

FIG. 2. Marginal hook of a G. rasini detached from a Xiphophorus hybrid. Note the pronounced curvature (arrowed) near the point of the sickle. (1 marker= 1mm).

FIG. 3. Schematic representations of the large cirrus spines of: (A) G. rasini from Xiphophorus hybrids; and (B) that of G. bullatarudis from P. reticulata. The three-dimensional curvature of these structures is not shown. The main di€erence between the two species is that each side of the base of the large cirrus spine of G. bullatarudis appears to join to form a ring whereas those of the large spine of G. rasini diverge and do not appear to join.

FIG. 4. (A±C) Cirrus armature of G. rasini from Xiphophorus hybrids ®xed and mounted in ammonium picrate±glycerin, viewed with a phase contrast microscope and drawn with the aid of a camera lucida.