The nutrition of sporocysts of the trematode Cercaria doricha Rothschild, 1935 in the molluscan host Turritella communis Risso

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Abstract
An investigation was carried out to discover how the sporocysts of Cercaria doricha obtain nutrients from their host Turritella and how castration of the snail is brought about.Histological studies of infected molluscan visceral humps showed no trace of toxic or mechanical damage by parasites. There appears to be an inverse relationship between the number of sporocysts and the amount of gonadial tissue.Biochemical analyses of molluscan tissues indicated that parasitized snails were not depleted of amino acids or purines. The concentration of plasma protein was higher in parasitized snails and the concentration of free amino nitrogen in head–foot muscle showed an increase of 7%. Histochemical investigations indicated that sporocysts do not remove glycogen from the molluscan connective tissue which surrounds them. The sporocysts appear to lack copious secretions of proteinase.The lack of conditions of starvation in parasitized specimens of Turritella, together with the great similarity of the free amino acid pools of sporocysts and molluscan gonad, suggests that the sporocysts obtain their food supply directly from the gonadial tubules. It is concluded that this is achieved by use of a placenta-like region of the sporocyst wall which is in contact with the gonadial tubule and which appears to be identical with the region of proliferation of the cercariae.This paper formed part of a thesis for the degree of Doctor of Philosophy in the University of Reading. I wish to thank the Science Research Council and the University of Reading for financial awards, and Professor Alistair Graham for encouragement and guidance during the work.

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