The Emergence of the Cercariae of Fasciola hepatica from the Snail Limnaea truncatula.

Abstract

1. Observations on Fasciola hepatica in Limnaea truncatula under laboratory conditions showed that the cercariae did not emerge at temperatures below 9°C. Above 9°C. emergence proceeded indiscriminately up to the limit of experimental observation (26°C).2. Experience showed that emergence occurred in the light or in darkness while changes in the hydrogen-ion concentration of the water containing the snails (within the range 5.5 to 8.5) had no effect on emergence. There was some evidence that an increase of carbondioxide in the water slowed but did not inhibit emergence but depletion of oxygen had no apparent effect.3. In the laboratory, emergence could be induced by removing snails from dry habitats and immersing them in water or by removing snails from watery habitats and placing them in fresh water. We were unable to determine the exact physical.or chemical factors acting as a stimulus under such conditions.

Influence of low temperatures on the cercarial shedding ofParamphistomum daubneyifrom the snailLymnaea truncatula

“…This finding contrasts with the reports by several authors. According to Kendall & McCullough (1951), there was no evidence of any significant differences in the numbers of F. hepatica cercariae which emerged from snails kept between 9°C and 26 °C. Inversely, in another parasite snail-system such as that studied by Schmidt & Fried (1996), the number of Echinostoma trivolvis cercariae, which emerged from naturally-infected Helisoma trivolvis, was significantly lower in snails kept at a constant temperature of 12°C compared to the controls at 28-29 °C.…”

Desenvolvimento de Eurytrema coelomaticum (Giard & Billet) (Digenea, Dicrocoeliidae) em Bradybaena similaris (Férussac) (Gastropoda, Xanthonychidae)

“…Embora estes autores tenham se referido ao "sistema sanguíneo" como principal rota de migração dos estágios larvais de trematódeos digenéticos em seus hospedeiros moluscos (BRUMl'T 1941 ;KENDALL & MCCULLOUGH 1951;PROBERT & ERASMUS 1965;KOZUTSUMI & iTAGAKI 1989), o sistema circulatório dos moluscos é semi-aberto, a hemolinfa: circula também, por espaços (lacunas) existentes entre os órgãos internos e não exclusivamente por ductos ou canais, como foi sugerido por estes autores. Dessa forma, a denominação "sistema hemolinfático" é a mais apropriada para designar o sistema circulatório dos moluscos.…”

L’infestation deLymnaea glabraMüller parFasciola hepaticaL.

“…-2) Les caractéristiques des émissions cercariennes n'ont été précisées que chez des L. truncatula adultes (Kendall et McCullough, 1951 ;Hodasi, 1972). Chez les autres espèces de limnées, les auteurs (Kendall, 1950 ;Berghen, 1964 ;Boray, 1966 ;Furmaga et Gundlach, 1969 ;Czapski, 1977) n'ont fourni que des valeurs sur le nombre de cercaires émis par ces limnées et la durée de leurs émissions ; de plus ces observations portent le plus souvent chez de jeunes limnées infestées.…”