242
MARINE MOLLUSCS AS HOSTS BOR SYMBIOSES
argentatus, although the rediae recovered 4 weeks after infection were
small and he was unable to determine whether these were mother or
daughter rediae. Cercariae escaping from naturally infected H . minuta
will penetrate and encyst in the palps and gills of Mya arenaria.
Tissues of naturally and experimentally infected M . arenaria were fed
to eider ducks, Somateria mollissima, herring gulls, Larus argentatus,
terns, Sterna hirundo, white mice and golden hamsters. Adults were
recovered from the intestine of the gull only. In the case of eider
ducks, the metacercariae were said to have excysted “ b u t did not
persist more than about 10 days.”
29. Himasthla littorinae Stunkard, 1966
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
In his report of the life cycle of Himasthla littorinae, a trematode
which will develop to maturity in experimentally infected herring gulls,
Larus argentatus, Stunkard (1966) stated that this parasite will encyst,
as metacercariae, in the palps, gills and mantle of Mytilus edulis, Mya
arenaria and in species of Littorina.
Description of metacercaria (the stage found in commercially
important molluscs). Cysts average 0.26 mm in diameter, with laminated wall which measures 0.005-0.006 mm in thickness. A complete
description of the metacercaria was not given by Stunkard ; however,
since the body of the cercaria is 0.45-0-85 mm long x 0.20-0-30 mm
wide, and the adult is 2.8-5.4 mm long x 0.41 mm wide, the dimensions
of the metacercaria must fall between these limits. Furthermore, since
both the cercaria and the adult possess twenty-nine collar spines
which are similarly arranged, it can be assumed that the metacercaria
also possesses twenty-nine spines arranged in a single curved row
except at the ventral ends where the last spine is flanked on each side
by a smaller spine set slightly more posteriorly. The larger collar
spines of the metacercaria are 0.029 mm long and 0.006 mm wide at
their bases.
According to Stunkard, the cercariae-bearing rediae
are found in Littorina saxatilis and L. obtusata taken near Woods
Hole, Massachusetts. Cercariae escaping from the gastropod first
intermediate host will penetrate and encyst in the molluscs mentioned,
including specimens of Littorina spp. from which the cercariae had
emerged. Metacercariae from the molluscan second intermediate host
will develop into adults in Larus argentatus but not domestic ducklings.
Life cycle.
MARINE MOLLUSCS AS HOSTS BOR SYMBIOSES
argentatus, although the rediae recovered 4 weeks after infection were
small and he was unable to determine whether these were mother or
daughter rediae. Cercariae escaping from naturally infected H . minuta
will penetrate and encyst in the palps and gills of Mya arenaria.
Tissues of naturally and experimentally infected M . arenaria were fed
to eider ducks, Somateria mollissima, herring gulls, Larus argentatus,
terns, Sterna hirundo, white mice and golden hamsters. Adults were
recovered from the intestine of the gull only. In the case of eider
ducks, the metacercariae were said to have excysted “ b u t did not
persist more than about 10 days.”
29. Himasthla littorinae Stunkard, 1966
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
In his report of the life cycle of Himasthla littorinae, a trematode
which will develop to maturity in experimentally infected herring gulls,
Larus argentatus, Stunkard (1966) stated that this parasite will encyst,
as metacercariae, in the palps, gills and mantle of Mytilus edulis, Mya
arenaria and in species of Littorina.
Description of metacercaria (the stage found in commercially
important molluscs). Cysts average 0.26 mm in diameter, with laminated wall which measures 0.005-0.006 mm in thickness. A complete
description of the metacercaria was not given by Stunkard ; however,
since the body of the cercaria is 0.45-0-85 mm long x 0.20-0-30 mm
wide, and the adult is 2.8-5.4 mm long x 0.41 mm wide, the dimensions
of the metacercaria must fall between these limits. Furthermore, since
both the cercaria and the adult possess twenty-nine collar spines
which are similarly arranged, it can be assumed that the metacercaria
also possesses twenty-nine spines arranged in a single curved row
except at the ventral ends where the last spine is flanked on each side
by a smaller spine set slightly more posteriorly. The larger collar
spines of the metacercaria are 0.029 mm long and 0.006 mm wide at
their bases.
According to Stunkard, the cercariae-bearing rediae
are found in Littorina saxatilis and L. obtusata taken near Woods
Hole, Massachusetts. Cercariae escaping from the gastropod first
intermediate host will penetrate and encyst in the molluscs mentioned,
including specimens of Littorina spp. from which the cercariae had
emerged. Metacercariae from the molluscan second intermediate host
will develop into adults in Larus argentatus but not domestic ducklings.
Life cycle.