Megalophallus deblocki n. sp. (Digenea: Microphallidae) from Rostrhamus sociabilis (Vieillot) (Aves: Accipitridae) in Paraguay Aneta Kostadinova 1, *, Claude Vaucher 2 & David I. Gibson 3 1 Department of Biodiversity, Central Laboratory of General Ecology, Bulgarian Academy of Sciences, 2 Gagarin Street, 1113, Sofia, Bulgaria 2 Museum d’Histoire Naturelle, CP 6434, CH-1211, Geneva 6, Switzerland 3 Department of Zoology, Natural History Museum, Cromwell Road, London, SW7 5BD, UK Accepted for publication 3rd May, 2005 Abstract A new species in the little-known digenean fauna of Paraguayan birds is described in detail, especially in relation to its terminal genitalia. The new form, Megalophallus deblocki n. sp., is a microphallid from the intestine of the snail kite Rostrhamus sociabilis (Vieillot). It is differentiated in detail from its congeners, but differs mainly in having a substantially larger phallus (e.g. in relation to the ventral sucker), a smaller ventral sucker and smaller eggs. Comments are included on the functional morphology of the terminal genitalia. Introduction This is the second paper (see Kostadinova, Vau- cher & Gibson, 2002) in a short series of studies on the trematodes obtained during a parasitological survey of birds from Paraguay carried out by the Museum of Natural History, Geneva. Apart from the work of Dubois (1988) on strigeoids, there appear to have been few previous studies on the trematodes from Paraguayan birds. Masi Pallare´s & Benı´tez Usher (1973) list only six species. The present work contains a description of a new species of the microphallid genus Megalophallus Cable, Connor & Balling, 1960 from the snail kite Rostrhamus sociabilis (Vieillot) (Accipitridae). Materials and methods Worms were fixed in hot 4% neutral formaldehyde and stored in 75% ethanol. They were stained with Mayer’s paracarmine, dehydrated in an ethanol series, cleared with Eugenol and mounted in Can- ada balsam. Measurements of the holotype are given in the description, with the mean ± standard deviation (SD) and range for the paratypes pre- sented in Table 1. All measurements and scales are in micrometres. Megalophallus deblocki n. sp. Type-host: Rostrhamus sociabilis (Vieillot), the snail kite or gavila´n caracolero (Aves: Ciconiifor- mes: Accipitridae). Type-locality: Host shot at km 204 on the Trans- chaco Road to Bolivia, Prov. Presidente Hayes, Paraguay; 7.xi.1987. Site: Intestine. Type-material: Museum d’Histoire Naturelle, Gen- eva, holotype 34496 INVE and paratypes 34497 INVE (all on one slide). Etymology: The species is named for Professor Ste´phane Deblock, University of Lille, France, in recognition to his major contributions to micro- phallid taxonomy. Description (Figures 1–5, Table 1) Based on whole-mounts of 8 specimens. Body minute, 534Â 296, dorso-ventrally flattened, with maximum width at level of ventral sucker or *Author for correspondence (E-mail: akk@ecolab.bas.bg) Systematic Parasitology (2006) 63:119–126 Ó Springer 2006 DOI 10.1007/s11230-005-9005-7