The species of larval Echinostomatidae that infect Biomphalaria straminea (Dunker, 1848) in a ricefield in Corrientes province, Argentina, were studied. Examination of 5 510 snails during 2 rice cultivation cycles, from December 2010 to May 2011 and from December 2011 to April 2012, revealed the presence of 3 new species: Echinocercaria sp. XIII, Echinocercaria sp. XIV and Echinocercaria sp. XVI in 36 snails (0.65%). The most common species was Echinocercaria sp. XVI. Prevalence of 3 species during the first rice cultivation cycle was low (< 1%), whereas during the second rice cultivation cycle it was somewhat higher, with prevalence greater than 1% only in Echinocercaria sp. XVI. The species of echinocercariae in B. straminea from the agricultural habitat described in the present study are new additions to the species already reported for the genus Biomphalaria in the region.

Se estudiaron las especies de echinocercarias que infectan a Biomphalaria straminea (Dunker, 1848) en un campo de arroz de la provincia de Corrientes, Argentina. La prospección de 5 510 caracoles durante 2 ciclos de cultivo de arroz, desde diciembre de 2010 a mayo de 2011 y desde diciembre de 2011 a abril de 2012, reveló la presencia de 3 nuevas especies: Echinocercaria sp. XIII, Echinocercaria sp. XIV y Echinocercaria sp. XVI en 36 caracoles (0.65%). La especie más común fue Echinocercaria sp. XVI. Durante el primer ciclo de cultivo de arroz las prevalencias de las 3 especies fueron bajas (< 1%), mientras que durante el segundo ciclo de cultivo de arroz las prevalencias fueron algo mayores, con valores superiores al 1% solo en Echinocercaria sp. XVI. Las especies de echinocercarias descritas en el presente estudio parasitando a B. straminea de un ambiente agrícola, se adicionan al registro de especies para el género Biomphalaria en la región.

A total of 3 494 snails from Biomphalaria straminea (Dunker, 1848) were collected from December 2010 to May 2011, in a ricefield in Corrientes province, Argentina, and 5 species of larval trematodes belonging to Strigeidae (Furcocercaria sp. XIV, Furcocercaria sp. XV, Furcocercaria sp. XVI), Diplostomidae (Furcocercaria sp. XVII) and Schistosomatidae (Furcocercaria sp. XVIII) found in 115 snails (3.29%) are described. Prevalence of infection ranged between 0.11% (e.g., Furcocercaria sp. XVIII) and 4.22% (e.g., Furcocercaria sp. XVI) in the snails examined. Furcocercaria sp. XIV, Furcocercaria sp. XV and Furcocercaria sp. XVI were the most common species present in nearly all months of the sampling period, whereas Furcocercaria sp. XVII and Furcocercaria sp. XVIII were rarer species. Infection rates of most larval digeneans were highest in March. The species of furcocercariae in B. straminea from the agricultural habitat described in the present study are now added to the 4 species of furcocercariae already reported for the region from the genus Biomphalaria.

Un total de 3 494 caracoles de Biomphalaria straminea (Dunker, 1848) fueron recolectados desde diciembre de 2010 a mayo de 2011en una arrocera en la provincia de Corrientes, Argentina y 5 especies (Furcocercaria sp. XIV, Furcocercaria sp. XV, Furcocercaria sp. XVI, Furcocercaria sp. XVII y Furcocercaria sp. XVIII) encontradas en 115 caracoles (3.29 %) se describieron. La prevalencia de infección varió entre 0.11 % (Furcocercaria sp. XVIII) y 4.22 % (Furcocercaria sp. XVI) en los caracoles examinados. Furcocercaria sp. XIV, Furcocercaria sp. XV y Furcocercaria sp. XVI fueron las especies más comunes presentes en casi todos los meses del periodo de muestreo, mientras que Furcocercaria sp. XVII y Furcocercaria sp. XVIII fueron las especies más raras. Las tasas de infección de la mayoría de los digeneos larvales fueron altas en marzo. Las especies de furcocercarias descriptas en el presente estudio en B. straminea de un hábitat agrícola, se suman a las 4 especies de furcocercarias reportadas en la región para el género Biomphalaria.

The life cycle of the trematode Zygocotyle lunata (Diesing, 1836) is studied, beginning with cercariae from naturally infected Biomphalaria peregrina (d'Orbigny, 1835) and B. tenagophila (d'Orbigny, 1835) from Buenos Aires Province and Salta Province (Argentina), respectively. Adults were recovered from Gallus domesticus (Linnaeus, 1758) and Mus musculus (Linnaeus, 1758). Egg development lasted for 15-23 days at 23-24 C, and 10-12 days at 28-30 C; it was delayed after successive passages through mice, and ceased thereafter. In the snail, sporocysts, located beneath the mantle border, occurred up to 37 days post exposure (PE). Rediae invaded the entire snail body; developing cercarial bodies within rediae were recognized by the presence of a short tail, excretory canals, and eye-spot pigment. Cercariae emerged from snails as early as 20-26 days PE, encysting immediately on any substrate. These can be easily differentiated from those of Paramphistomum Fischoeder, 1901 spp. and Cotylophoron Stiles and Goldberger, 1910 spp., which have lateral excretory tubes forming a ring at the midlevel of the body and usually lack pharyngeal appendages. Metacercariae were infective for at least 6 months. Mature adults were observed 27-32 days PE in mice and 35 days PE in chicks. Biomphalaria tenagophila represents a new intermediate natural host record and Salta Province a new geographic area; Dendrocygna viduata (Linnaeus, 1766) and D. bicolor (Vieillot, 1816) from Venezuela are new host records for Z. lunata.

El ciclo de vida del trematode Zygocotyle lunata (Diesing, 1836) (Paramphistomoidea: Zygocotylidae) fue estudiado experimentalmente, comenzando con cercarias emergidas de Biomphalaria peregrina (d'Orbigny, 1835) y B. tenagophila (d'Orbigny, 1835) infectadas naturalmente, provenientes de las provincias de Buenos Aires y Salta (Argentina), respectivamente. Los adultos fueron obtenidos de Gallus domesticus (Linnaeus, 1758) y Mus musculus (Linnaeus, 1758). El desarrollo del huevo demora 15-23 días a 23-24 C y 10-12 días a 28-30 C; demora aun más después de sucesivos pasajes por ratones, no desarrollándose posteriormente. Los esporoquistes se localizan debajo del borde del manto del molusco, y se observaron hasta 37 días después de la infección (PE). Las redias invaden todo el cuerpo del molusco; los cuerpos de las cercarias en desarrollo se distinguen por la presencia de una cola corta, canales excretores y pigmento de manchas oculares. Las cercarias emergen como mínimo después de 20-26 días PE y se enquistan inmediatamente sobre cualquier superficie. Pueden ser fácilmente diferenciadas de las cercarias de Paramphistomum Fischoeder, 1901 spp. y Cotylophoron Stiles and Goldberger, 1910 spp., las cuales poseen canales excretores laterales formando un anillo a nivel medio del cuerpo, y generalmente no poseen apéndices faringeales. Las metacercarias son infectivas al menos hasta 6 meses. Adultos maduros fueron observados a partir de 27-32 días PE en los ratones y 35 días PE en los pollos. Biomphalaria tenagophila constituye un nuevo hospedador intermediario natural y la Provincia de Salta un área geográfica nueva; Dendrocygna viduata (Linnaeus, 1766) y D. bicolor (Vieillot, 1816) de Venezuela constituyen nuevos hospedadores definitivos de Z. lunata.

The molluscs Heleobia castellanosae and Ampullaria canaliculata and cichlid fishes were collected from an artificial pond at Tres de Febrero Park (Buenos Aires city), between June 1994 and May 1995. One hundred and eighty of 2,467 H. castellanosae examined were infected with pre-adults of Lobatostoma jungwirthi, 112 of them in concurrent infections with digeneans. L. jungwirthi was significantly more prevalent in larger snails, especially those infected with larval digeneans, but the prevalence of infection did not fluctuate significantly throughout the year. A. canaliculata and cichlids smaller than 10 cm were not infected, but larger Cichlasoma facetum harboured adults of L. jungwirthi in their intestines. Experimental infections of C. facetum and Gymnogeophagus meridionalis with pre-adult aspidogastreans obtained from H. castellanosae were successful. The development of L. jungwirthi in the snail host involves five arbitrary growth phases. Its life-cycle is heteroxenous, similar to that described for L. manteri, with H. castellanosae as the intermediate host and cichlid fishes as the definitive host in this pond.

The life cycle of Pygidiopsis crassus n. sp. was experimentally reproduced, starting from cercariae from naturally infected Littoridina parchappei collected from Lujan River and different ponds in Buenos Aires Province, Argentina. Metacercariae were found encysted in the body cavity of experimentally and naturally infected fishes Cnesterodon decemmaculatus and naturally infected Jenynsia lineata. Adults were obtained experimentally in chicks and mice. The natural host is unknown. The new species is compared with Pygidiopsis macrostomum Travassos 1928, from Rattus norvegicus and from Noctilio leporinus mastivus, differing in body and egg sizes, in the size relation of oral and ventral sucker and the shape of excretory vesicle.