244
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
out experimental life cycle studies, believed that P. acanthus and P.
avitus are distinct and that the cercaria described by Stunkard and Shaw
(1931) as Cercaria sensifera is the larva of P. avitus.
P. acanthus is mentioned in connection with parasites of commercially
important marine molluscs since its cercaria, originally described as
Cercaria purpurae by Lebour (1907c, 1911) from Nucella ( = Purpura)
hpillus from British waters, was reported by Lebour and Elmhirst
(1922) to penetrate and encyst in the mantle and foot of either Cardiunz
edule or Mytilus edulis. Their observations have been criticized by
Stunkard and Shaw (1931) and Stunkard and Cable (1932) who have
shown that the cercaria of P. acanthus does not penetrate pelecypods
but encysts on the body surface.
The observation by Stunkard and his co-workers has been strengthened by the observation of F. G . Rees (1939b, 1940) who has studied
the early stages of P. acanthus in great detail. She has demonstrated
that cercariae maintained in aquaria will encyst on the outside of
Nucella shells and on other objects. Similarly, Xtunkard and Cable
(1932) have found that the cercariae would encyst on the shells of
Mytilus which are placed in a container with cercariae. They also
have reported that :
In one case, three cysts were found on the surface of the foot and mantle, and
a few others were seen in masses of mucus in the mantle cavity. In the same
specimen, large numbers of cercariae encysted on the outside of the shell,
most of them near the incurrent siphon. Many of them struck the shell
around the incurrent opening, adhered, and immediately encysted.
It is now known that P. acanthus cercariae will encyst on practically
any surface and that mechanical stimulation, such as stirring or shaking,
accelerates encystment (Stunkard and Cable, 1932). In nature, it is
possible that birds become infected with the ingestion of Cardiunz
edule, Mytilus edulis, or other molluscs with encysted metacercariae
attached to their surfaces.
Description of metacercaria (the stage which may encyst on the
body surface of commercially important molluscs). Cyst fairly transparent, comprised of two walls, an outer thick and brittle one, and an
inner thin and tough one; flat on the attached side; fluid in space
between metacercaria and host sometimes contains small granules
which, according to Xtunkard and Cable (1932), probably represent
materials discharged from the metacercaria’s excretory system.
Metacercaria with collar armed with forty-eight spines ; doubled over
ventrally ; motile for several hours after encystment. A detailed
description of this metacercaria is not yet available.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
out experimental life cycle studies, believed that P. acanthus and P.
avitus are distinct and that the cercaria described by Stunkard and Shaw
(1931) as Cercaria sensifera is the larva of P. avitus.
P. acanthus is mentioned in connection with parasites of commercially
important marine molluscs since its cercaria, originally described as
Cercaria purpurae by Lebour (1907c, 1911) from Nucella ( = Purpura)
hpillus from British waters, was reported by Lebour and Elmhirst
(1922) to penetrate and encyst in the mantle and foot of either Cardiunz
edule or Mytilus edulis. Their observations have been criticized by
Stunkard and Shaw (1931) and Stunkard and Cable (1932) who have
shown that the cercaria of P. acanthus does not penetrate pelecypods
but encysts on the body surface.
The observation by Stunkard and his co-workers has been strengthened by the observation of F. G . Rees (1939b, 1940) who has studied
the early stages of P. acanthus in great detail. She has demonstrated
that cercariae maintained in aquaria will encyst on the outside of
Nucella shells and on other objects. Similarly, Xtunkard and Cable
(1932) have found that the cercariae would encyst on the shells of
Mytilus which are placed in a container with cercariae. They also
have reported that :
In one case, three cysts were found on the surface of the foot and mantle, and
a few others were seen in masses of mucus in the mantle cavity. In the same
specimen, large numbers of cercariae encysted on the outside of the shell,
most of them near the incurrent siphon. Many of them struck the shell
around the incurrent opening, adhered, and immediately encysted.
It is now known that P. acanthus cercariae will encyst on practically
any surface and that mechanical stimulation, such as stirring or shaking,
accelerates encystment (Stunkard and Cable, 1932). In nature, it is
possible that birds become infected with the ingestion of Cardiunz
edule, Mytilus edulis, or other molluscs with encysted metacercariae
attached to their surfaces.
Description of metacercaria (the stage which may encyst on the
body surface of commercially important molluscs). Cyst fairly transparent, comprised of two walls, an outer thick and brittle one, and an
inner thin and tough one; flat on the attached side; fluid in space
between metacercaria and host sometimes contains small granules
which, according to Xtunkard and Cable (1932), probably represent
materials discharged from the metacercaria’s excretory system.
Metacercaria with collar armed with forty-eight spines ; doubled over
ventrally ; motile for several hours after encystment. A detailed
description of this metacercaria is not yet available.