Ancyrocephalid (Monogenea) of freshwater fish, Oligosarcus jenynsii (Characidae), from shallow lake of the Pampasic region Argentina, with the erection of two new genera

ROSSIN, M. ALEJANDRA; TIMI JUAN TOMÁS

Rio de Janeiro

Simposio; 7th Iternational Symposium on Monogenea; 2013

Universidad Federal Do Paraná, Instituto Oswaldo Cruz,Universidad Federal Rural Do Rio de Janeiro

The Pampasic region, central Argentina, is characterized by the presence of numerous shallow lakes (approximately 1430). Buenos Aires province is located at the south east and comprises large proportion of this region. About 8 species of Characidae inhabit lakes and streams of this region, although their systematics is currently under revision. One of them is Oligosarcusjenynsii, a pelagic, widely distributed and dominant species in most ecosystems. During a parasitological examination of O. jenynsii captured at Nahuel Rucá lake (Buenos Aires province, Argentina) during 2012-2013, ancyrocephalid monogeneans were found in the gills. This group of parasites has been poorly studied in characid fish from Argentina. To date only 2 species belonging to the genus Palombitrema have been reported from this family of hosts from Chascomus Lake (Buenos Aires province), P. heteroancistrium and P. chascomusensis parasites of Astyanax fasciatus and O. jenynsii, respectively. However, P. chascomusensis was firstly described in the genus Androspira from Cyphocharax voga, a member of the related characiform family Curimatidae. Androspira was erected to accommodate it together with the type species A. triangula, described simultaneously. Both species were later transferred to the genus Palombitrema. A close examination of ancyrocephalid monogeneans of O. jenynsii using standard parasitological procedures showed that they belonged to 4 species, one of them referable to P. chascomusensis. However, these specimens displayed a series of morphological features, such as marginal hooks similar in shape and size, accessory piece not composed by two subunits and base of male copulatory organ (MCO) articulated to accessory piece by a twisted articulation process lying within rings of MCO, that contrast with the generic diagnosis of Palombitrema. The combination of these characters, together with ventral anchors longer than dorsal anchors, ventral and dorsal bars V-shaped with expanded terminations, ventral bar with slight posterior medial indentation, 14 marginal hooks with dilated shank, MCO as a coiled tube with counter-clockwise rings and sclerotized sinistral vagina, justified therefore the erection of a new genus, to which three of the species found in O. jenynsii were allocated. Morphological and morphometric differences of MCO, accessory piece, ventral and dorsal anchors, marginal hooks and vagina allowed the discrimination among the three congeners. On the other hand, the fourth species shares with Palombitrema a MCO as a coiled tube with counter-clockwise rings, an accessory piece composed by 2 subunits and a sclerotized sinistral vagina directed posteriorly, differing therefore from other genera. But, can be distinguished from Palombitrema by having marginal hooks of similar size and shape and the base of MCO articulated to accessory piece by a delicate ligament. Consequently a new genus is proposed for this species. All species are described and illustrations of sclerotized structures are provided.