First record of Helobdella hyalina ( Hirudinea ; Glossiphoniidae ) in the mantle cavity of Planorbidae from lentic environments in a Buenos Aires province , Argentina

Pasante Div. Zool. Invertebrados, Cátedra Zoología Invertebrados I, Facultad de Ciencias Naturales y Museo – FCNYM, Universidad Nacional de La Plata – UNLP b Cátedra Zoología Invertebrados I, FCNYM, Universidad Nacional de La Plata – UNLP Div. Zoología Invertebrados, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Investigador Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Paseo del Bosque, s/n, 1900 La Plata, Buenos Aires, Argentina


Introduction
Biomphalaria peregrina (D'Orbigny, 1835) and Drepanotrema kermatoides (D'Orbigny, 1835) were first reported as hosts of Helobdella hyalina Ringuelet, 1942.Both are important species from the Río de La Plata river basin in Argentina.They are associated with macrophytes of lentic or semilentic environments.They are more frequently observed in semipermanent low-depth environments with vegetation and abundant organic matter (Bonetto et al., 1990).
Several species of hirudinea Glossiphoniidae are, occasionally or permanently, present in these mollusks having trophic and non -trophic relationships with them (Ringuelet, 1985).

Materials and Methods
Specimens of Biomphalaria peregrina and Drepanotrema kermatoides (Planorbidae) were collected in permanently inundated areas or in those which are subjected to periodic inundations near the Lujan river, in the Reserva de Uso Multiple Otamendi (34° 17' S and 58° 53' W), Campana, Buenos Aires, Argentina.
Sampling was carried out during October, 2002 in the inundated areas where the espartillar community is composed of the totally dominant species Spartina densiflora, and aquatic vegetation such as Bacopa monnieri and Ludwigia peploides.
Planorbidae were anaesthetised with 0.01 g Nembutal and then fixed in phormol 5%.The hirudinea found in the mantle cavity were separated and assigned a specific level, determining if they were carrying eggs or young.

Results
Two hundred and sixty one specimens of D. kermatoides were examined, only one of them had a specimen of H. hyalina (prevalence: 0.38%).In addition, two hundred and twelve specimens of B. peregrina were analysed revealing 6 specimens of H. hyalina (prevalence: 2.35%); in only one case, two specimens of H. hyalina were found in only one snail.

Conclusion and Discussion
Helobdella hyalina has a specialised type of leech predation in which a proboscis sucks up body fluids and soft parts of an invertebrate prey organism.
H. hyalina appears to be an opportunistic species that have a trophic relationship with its host this is corroborated by the small number of hosts with leeches.This would suggest that the diet of H. hyalina is based on a variety of food items, including planorbids.
Further surveys must be carried out in order to determine if this kind of relationship is temporary or permanent and to establish if this relationship is exclusively trophic.