A study of digenean parasites from the salt marshes of North Norfolk.
Hanan El-Mayass, 1991. A study on digenean parasites from the
salt marshes of North Norfolk.
A survey of digenean parasites was conducted, particularly those
utilizing the gastropod Hydrobia ulnae as a first intermediate
host, on the salt marshes at Stiff key on the North Norfolk coast.
Thirteen species belonging to the Notocotylidae , Microphallidae,
Heterophyidae, Echinostomatidae and Gymnophallidae were
identified and redescribed. A study of the seasonal occurrence
of the most common digeneans in H. ulvae was conducted and
considered in relation to the biology and behaviour of their
hosts and the ecological conditions of their habitat. A study of
the effect of these parasites on H. ulvae collected from the
upper marsh and lower marsh was also conducted. The result of
this study showed that the adult snails from the lower marsh are
more infected than those from the upper marsh. There was no
relationship between parasitism and sex of the snail and no
parasite-induced gigantism was detected.
The ultrastructure of the cyst wall and the in vitro
excystation of three different species of metacercariae, namely,
Cryptocotyle concavum, Bucephalus haimeanus and Microphallus
Primas, were studied. C. concavum excysted most readily at 40-
42°C after pretreatment with acid pepsin in slightly alkaline
solutions containing bile salts, but they also emerged in saline
without treatment with enzymes or bile salts. There is evidence
that glands in the anterior region are used to penetrate the cyst
wall. B. haimeanus excysted in trypsin solutions at pH 7.8 at 20-
22°C. However, some metacercariae excysted and survived for more
than 2h in 1% pepsin at pH 2.0. Bile salts failed to stimulate
the metacercaria of B. haimeanus and played no part in
excystation. Excystment of M. primas occurred only in trypsin
solutions at pH 7.6 at 40-42°C. Egg production in the progenetic
metacercaria of M. primas, was studied and its initiation was
found to be temperature-dependent.