250
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Italy. He assigned it to the family Allocreadiidae. As far as I can
determine, it has not been found since.
Description. Cyst (Fig. 161) ovoid, transparent, 0.32 mm x 0.25mm.
Metacercaria (Fig. 161) elongate, 0.66 mm long x 0.20 mm wide,
covered with fine cuticular spines ; anterior sucker 0.1 1 mm in diameter ;
ventral sucker 0.092 mm in diameter ; relatively long prepharynx
present ; pharynx 0.063 mm long x 0.038 mm in diameter ; esophagus
approximately same length as prepharynx ; intestinal caeca reaching
into posterior one-fourth of body ; group of cephalic glands (Palombi
depicts nineteen) on each side of prepharynx, pharynx, and esophagus,
with ducts leading to margin of anterior sucker ; testicular primordia,
two in number, tandemly arranged in intercaecal space in posterior
one-third of body ; ovarian anlage situated between testes ; excretory
vesicle tubular, reaching posterior margin of ventral sucker.
Other information. If M . acherusiae is an allocread trematode, then
from our knowledge of the life cycle pattern within this family, the
definitive host is most probably a fish.
37. Metacercaria mytili sp. inq. Lebour, 1906. (Fig. 162)
(Taxonomic position undetermined)
This metacercaria, erroneously identified as a cercaria and originally
named Cercaria mytili, was described by Lebour (1906) encysted in the
digestive gland of Mytilus edulis from Northumberland and Cardium
edule from the west coast of Scotland, primarily in the former. It is
not possible even to attempt an identification of this larva from
Lebour's description and figure except that the two conspicuous lateral
main collecting tubules of the excretory system, which are filled with
granules, is suggestive of certain echinostome metacercariae, but
Lebour did not report the occurrence of a collar with spines which is
characteristic of echinostomes.
Description. Metacercarial cyst (Fig. 162) spherical, transparent,
0.20 mm in diameter. Metacercaria 0.46 mm long, covered with spines ;
posterior end pointed, anterior end rounded ; anterior and ventral
suckers about the same size, 0.06 mm in diameter; ventral sucker
immediately posterior of center of body ; two lateral tubules of excretory system conspicuous, full of clear granules.
38. Cercaria buccini sp. inq. Lebour, 1911. (Figs. 163 and 164)
(Taxonomic position undetermined)
Cercaria buccini is a microcercous cercaria described briefly by
Lebour (1911) from Buccinum undatum " brought in by the fishing
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Italy. He assigned it to the family Allocreadiidae. As far as I can
determine, it has not been found since.
Description. Cyst (Fig. 161) ovoid, transparent, 0.32 mm x 0.25mm.
Metacercaria (Fig. 161) elongate, 0.66 mm long x 0.20 mm wide,
covered with fine cuticular spines ; anterior sucker 0.1 1 mm in diameter ;
ventral sucker 0.092 mm in diameter ; relatively long prepharynx
present ; pharynx 0.063 mm long x 0.038 mm in diameter ; esophagus
approximately same length as prepharynx ; intestinal caeca reaching
into posterior one-fourth of body ; group of cephalic glands (Palombi
depicts nineteen) on each side of prepharynx, pharynx, and esophagus,
with ducts leading to margin of anterior sucker ; testicular primordia,
two in number, tandemly arranged in intercaecal space in posterior
one-third of body ; ovarian anlage situated between testes ; excretory
vesicle tubular, reaching posterior margin of ventral sucker.
Other information. If M . acherusiae is an allocread trematode, then
from our knowledge of the life cycle pattern within this family, the
definitive host is most probably a fish.
37. Metacercaria mytili sp. inq. Lebour, 1906. (Fig. 162)
(Taxonomic position undetermined)
This metacercaria, erroneously identified as a cercaria and originally
named Cercaria mytili, was described by Lebour (1906) encysted in the
digestive gland of Mytilus edulis from Northumberland and Cardium
edule from the west coast of Scotland, primarily in the former. It is
not possible even to attempt an identification of this larva from
Lebour's description and figure except that the two conspicuous lateral
main collecting tubules of the excretory system, which are filled with
granules, is suggestive of certain echinostome metacercariae, but
Lebour did not report the occurrence of a collar with spines which is
characteristic of echinostomes.
Description. Metacercarial cyst (Fig. 162) spherical, transparent,
0.20 mm in diameter. Metacercaria 0.46 mm long, covered with spines ;
posterior end pointed, anterior end rounded ; anterior and ventral
suckers about the same size, 0.06 mm in diameter; ventral sucker
immediately posterior of center of body ; two lateral tubules of excretory system conspicuous, full of clear granules.
38. Cercaria buccini sp. inq. Lebour, 1911. (Figs. 163 and 164)
(Taxonomic position undetermined)
Cercaria buccini is a microcercous cercaria described briefly by
Lebour (1911) from Buccinum undatum " brought in by the fishing