Gyrodactylus bullatarudis Turnbull, 1956

(Figures 3B, 6, 7, 8A ±C, 9C, D)

Voucher specimens: The Natural History Museum, London (BM(NH) 1994.11.24.1 ±6).

Host: Poecilia reticulata imported into UK from ornamental ®sh farms in Singapore. Site: external surface, anterior of ®sh, particularly head and opercula regions. A`very small’ species according to scheme of Harris (1985). Body length of moderately contracted living specimens under 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. The anterior and posterior pharyngeal bulbs of ¯attened specimens were of approximately equal width. Pharynx measurements were not taken. Measurements of attachment hooks and bars are given in table 1. The most distinctive elements were the connecting bars and the marginal hooks (see ®gures 6 and 7). The ventral bar had relatively long antero-lateral processes and a membrane which tapered slightly posteriorly. The dorsal bar had an obvious notch at the mid point with two swellings on either side (®gure 6). The marginal hook blade was bent at an angle of about 90ss with a straight point not extending as far as the toe. The cirrus had one large spine with the base on each side curved behind and joined (®gure 3B) and a single row of four to seven small spines (®gure 8).

Gyrodactylus bullatarudis from P. reticulata infected and reproduced on seven Xiphophorus hybrids. An increasing G. bullatarudis infrapopulation caused the death of one Xiphophorus, but six infrapopulations went extinct between one and ten days af ter infection (®gure 10).