Systematic Parasitology 48: 41–45, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 41 Salsuginus neotropicalis n. sp. (Monogenea: Ancyrocephalinae) from the pike killifish Belonesox belizanus (Atheriniformes: Poeciliidae) from southeastern Mexico E. F. Mendoza-Franco & V. M. Vidal-Mart´ ınez Laboratory of Parasitology, Centre for Research and Advanced Studies, National Polytechnic Institute (CINVESTAV-IPN, Merida Unit), Carretera Antigua a Progreso km. 6, AP 73 ‘Cordemex’, CP 97310 M´ erida, Yucat´ an, M´ exico Accepted for publication 21st February, 2000 Abstract Salsuginus neotropicalis n. sp. is described from the gills of Belonesox belizanus (Kner), the pike killifish (Poecili- idae), from the southeastern Mexico. S. neotropicalis is distinguished from all other congeners by the morphology of the haptoral sclerites, especially by the presence of a ventral bar with notably enlarged ends, and by possessing overlapping gonads. The diagnosis of Salsuginus is amended based on the position of gonads in this species. This is the first known Salsuginus species occurring in a freshwater fish from the Neotropical Region. Introduction Most members of Salsuginus Beverley-Burton, 1984 have been described from the gills of North American cyprinidontiform fish belonging to the genus Fundu- lus Lacepède (see Beverley-Burton, 1984; Murith & Beverley-Burton, 1985; Rand & Wiles, 1987; Janovy et al., 1989; Ferdig et al., 1991). Other records of Salsuginus spp. have been in species of Cyprinodon Lacepède and Gambusia Poey from the Bahamas and Bermuda, respectively (Hanek & Fernando, 1972; Murith & Beverley-Burton, 1985; Rand & Wiles, 1987). During studies on the parasites of fish carried out in Yucatan between September, 1996 and May, 1999, monogeneans belonging to Salsuginus were found on the gills of the poeciliid Belonesox belizanus (Kner). Since these worms represent a new, hitherto unde- scribed species of Salsuginus, they are described in this paper. Materials and methods Belonesox belizanus were collected using a cast net from Chaamac cenote (= sinkhole) (20 ◦ 51 ′ 53 ′′ N; 90 ◦ 09 ′ 18 ′′ W), situated inland about 30 km west of the coast of the Yucatan Peninsula, Mexico during September, 1996. Fish were brought alive to the lab- oratory, where they were killed and examined for monogeneans. Worms were observed and measured as temporary or permanent mounts fixed with ammo- nium picrate (Ergens, 1969) for study of the hard parts or sclerotized structures. In addition, some specimens were fixed with hot 4% formaldehyde, stained with Gomori’s trichrome and mounted in Canada balsam. Measurements are in micrometres (μm); the mean is followed by the range and number (n) of speci- mens measured in parentheses. Drawings were made with the aid of an Olympus microscope drawing at- tachment. Specimens were deposited in the Colección Nacional de Helmintos (CNHE), Institute of Biology, National Autonomous University of Mexico, Mex- ico; the United States National Parasite Collection, Beltsville, Maryland (USNPC); and the Laboratory of Parasitology, at Centre for Research and Advanced Studies, National Polytechnic Institute (CINVESTAV- IPN), Mérida, Mexico (CHCM).