Wallinia chavarriae n. sp. (Trematoda: Macroderoididae) in Astyanax aeneus (GÃ1⁄4nther, 1860) and Bryconamericus scleroparius (Regan, 1908) (Osteichthyes: Characidae) from the Ærea de ConservaciÃ3n Guanacaste, Costa Rica

Wallinia chavarriae n. sp. is described from the small-bodied characids Astyanax aeneus and Bryconamericus scleroparius in the Area de Conservacion Guanacaste, northwestern Costa Rica. The species differs from W. valenciae in possessing an acetabulum that is smaller than the oral sucker and vitelline follicles that are ovoid or rounded rather than elongate and tubular. Detailed comparison between these 2 species is handicapped by the less than satisfactory condition of the type and only museum specimen of W. valenciae. Wallinia chavarriae and W. valenciae belong to a subfamily of trematodes, Walliniinae, that arguably includes Creptotrematina spp., Magnivitellum simplex, and possibly Margotrema. The morphology of walliniines suggests that they are macroderoidids, but a clearer understanding of their classification could be gained from their larval morphology or from molecular systematic studies. The host associations of a monophyletic Walliniinae would indicate diversification within 2 groups of freshwater fishes: the neotropical characids for species of Wallinia, Creptotrematina, and Magnivitellum and the endemic central Mexican goodeids for those of Margotrema. The biogeography and host associations of these parasites provide a system for studies of potential host switching and vicariance, involving the middle-American and neotropical regions. The parasites of freshwater fishes in Central America are poorly known. Previous studies are limited to surveys of selected fishes in Nicaragua (Watson, 1976; Aguirre-Macedo et al., 2001) and a few scattered reports of some other parasite species (Sogandares-Bernal, 1955; Caballero and Brenes, 1957; Brenes, 1961; Bravo-Hollis and Arroyo, 1962; Vidal-Martinez et al., 2001). Of these, the reports by Caballero and Brenes (1957) of the trematode Acanthostomum minimum Stunkard, 1937, and by Bravo-Hollis and Arroyo (1962), of 2 Crassicutis spp. appear to be the only records of freshwater fish parasites from Costa Rica. During June 1998, freshwater fishes from the Area de Conservaci6n Guanacaste (ACG) in northwestern Costa Rica were examined as part of an ongoing biodiversity inventory of the eukaryotic parasites of vertebrates in this area (Brooks and Hoberg, 2000; Brooks et al., 2000). During that study, the 2 common species of characids encountered, Astyanax aeneus (Gtnther, 1860) and Bryconamericus scleroparius (Regan, 1908), were found to host a hitherto undescribed species of Wallinia Pearse, 1920, which is described here. MATERIALS AND METHODS The characids Astyanax aeneus (Giinther, 1860) and Bryconamericus scleroparius (Regan, 1908) were caught in Rio Sapoa (34 A. aeneus, 18 B. scleroparius) and Quebrada Limonal (16 B. scleroparius only) between 6 June and 19 June, 1998; all sampling sites were within the ACG, Guanacaste Province, Costa Rica. Other species of fish (sample sizes in parentheses) examined from Rio Sapoa during the same period were: Brycon guatemalensis Regan, 1908 (2), Astatheros alfari (Meek, 1907) (6), Parachromis dovii (Giinther, 1864) (21), Archocentrus nigrofasciatus (Giinther, 1867) (17), Gobiomorus dormitor Lacepede, 1800 (1), Hypsophrys nicaraguaensis (Ginther, 1864) (16); Neetroplus nematopus Giinther, 1867 (26), Poecilia gillii (Kner, 1863) (13), Rhamdia guatemalensis (Giinther, 1864) (2), Rhamdia rogersi (Giinther, 1864) (20). In addition, 26 A. alfari, 3 A. nigrofasciatus, 1 Phallichthys Received 27 February 2001; revised 30 May 2001; accepted 1 June 2001. * Present address: Division of Natural Sciences, John Minahan Science Hall, St. Norbert College, 100 Grant Street, De Pere, Wisconsin 54115. t Norwegian Institute for Nature Research, Tungasletta 2, 7485 Trondheim, Norway. t Department of Zoology, University of Toronto, Toronto, Ontario M5S 3G5, Canada. amates (Miller, 1907) and 5 R. rogersi were also examined from Quebrada Limonal. Fish were caught with gillnets or by electroshocking, brought back to the laboratory at the Centro de Investigacion of the ACG's Santa Rosa field station, and examined within 1-4 hr of capture. The parasites were recovered live, washed briefly in 0.6% saline, killed by rapid immersion in steaming hot water, and transferred immediately to alcohol-formalin-acetic acid (AFA) or killed and fixed simultaneously in steaming hot 5% formalin, accompanied by brief, vigorous shaking (see also Platt, 2000a, 2000b). The digeneans were stained with acetocarmine, dehydrated, and mounted in balsam on slides or between 2 cover slips. The double cover slip preparations were mounted in aluminum Cobb slides. Specimens were examined using bright-field and differential interference contrast optics on a Nikon BX 50 microscope. Illustrations were made with a drawing tube attached to the microscope. The following museum specimens were examined (accession numbers are preceded by the acronyms of the museum of their origin): Wallinia valenciae Pearse 1920, USNPC 7569 (holotype); Creptotrematina aguirrepeqenoi, ex Astyanax fasciatus mexicanus, San Marcos River, Texas (loan from Norman Dronen, Texas A&M University); Creptotrema dispar de Freitas, 1941 (= Creptotrematina dispar), CHIOC 15.357; Creptotrema dissimilis de Freitas, 1941 (= Creptotrematina dissimilis), CHIOC 10.720; Margotrema bravoae Lamothe-Argumedo, 1970, CNHE 869, 1594. USNPC is the U.S. National Parasite Collection, Beltsville, Maryland; HWML is the Harold W. Manter Laboratory of Parasitology, University of Nebraska, Lincoln, Nebraska; CHIOC refers to Colecao Helmintologica, Instituto Oswaldo Cruz, Rio de Janeiro, Brazil; and CNHE is the Collecion Nacional de Helmintos, Universidad Nacional Aut6noma de Mdxico, Mexico City, Mexico. In addition, 2 Magnivitellum simplex, ex Astyanax fasciatus from Nocchon-chunchey (Nicaragua) were examined (loan from Leopoldina Aguirre-Macedo, CINVESTAV, Merida, Mdxico). Measurements are given in micrometers (ptm) and are expressed as the mean ? SD, followed by the range in parentheses. Measurements are from 11 specimens unless otherwise mentioned.