6. THE PHYLA PORIFERA, ONIDARIA AND PLATYHELMINTHES
227
Description. Metacercariae (Fig. 137) vary greatly in size, 0.120-20 mm long, width ordinarily about one-half length but length and
width may be subequal when contracted while the width may be onefourth the length when extended ; body covered with cuticular spines ;
anterior sucker 0.147-0.160 mm in diameter (in large specimens) ;
ventral sucker in posterior half of body, 0.13-0.14 mm in diameter (in
large specimens) ; anterior body region with several small papillae,
each tipped with short stiff bristle ; large number of unicellular glands
in region of and opening into anterior sucker ; prepharynx absent,
pharynx and esophagus of median length present ; intestinal caeca
reaching level of anterior margin of ventral sucker, lined with large
cells with yellow granules intracellularly and intraluminally ; excretory
vesicle Y-shaped, with arms extending to posterior level of pharynx ;
flame-cell pattern 2[(2 + 2 + 2) + (2 + 2 + 2)].
Life cycle. Stunkard and Uzmann (1958) have fed this metacercaria
to mice, hamsters, eider ducks, and herring gulls but failed to recover
adults. The life cycle of this metacercaria remains undetermined.
Other information. It is known that Metacercaria I actively ingests
materials from the host’s mantle. Furthermore, Stunkard and Uzmann
have stated : “ The yellow material (in caecal cells and lumen) appears
like that in the digestive gland of the clam and may be taken by the
parasite from the vascular fluid of the mollusk.”
19. Cercaria myae Uzmann, 1952. (Fig. 138)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
Cercaria myae was originally described by Uzmann (1952) from the
soft clam, Mya arenaria, collected in the vicinity of Newburyport,
Massachusetts. It has been subsequently found in the same host
collected at Boothbay Harbor, Maine (Stunkard and Uzmann, 1958),
and I (unpublished) have found it in the same clam in Narragansett
Bay, Rhode Island.
Description of stages in mollusc. Sporocyst motile, unpigmented,
clavate, occupying interfollicular spaces of gonad and interlobular
spaces of digestive gland of host, few throughout haemocoel, with thin
wall and birthpore at apical end; 0.21-0.60 mm long. Cercaria (Fig.
138) small, elongate ovoid, furcocercous ; body proper 0.12-0.25 mm
long ; tail stem short, about one-third body length, slightly shorter than
furcae ; body covered with minute spines, each 0.001 mm long ; delicate
setae on posterior surfaces of furcae ; anterior sucker 0.039-0-052 mm
in diameter ; ventral sucker 0-040-0.046 mm in diameter ; prepharynx
superfamily Fellodistomatoidea ; family Fellodistomatidae)
227
Description. Metacercariae (Fig. 137) vary greatly in size, 0.120-20 mm long, width ordinarily about one-half length but length and
width may be subequal when contracted while the width may be onefourth the length when extended ; body covered with cuticular spines ;
anterior sucker 0.147-0.160 mm in diameter (in large specimens) ;
ventral sucker in posterior half of body, 0.13-0.14 mm in diameter (in
large specimens) ; anterior body region with several small papillae,
each tipped with short stiff bristle ; large number of unicellular glands
in region of and opening into anterior sucker ; prepharynx absent,
pharynx and esophagus of median length present ; intestinal caeca
reaching level of anterior margin of ventral sucker, lined with large
cells with yellow granules intracellularly and intraluminally ; excretory
vesicle Y-shaped, with arms extending to posterior level of pharynx ;
flame-cell pattern 2[(2 + 2 + 2) + (2 + 2 + 2)].
Life cycle. Stunkard and Uzmann (1958) have fed this metacercaria
to mice, hamsters, eider ducks, and herring gulls but failed to recover
adults. The life cycle of this metacercaria remains undetermined.
Other information. It is known that Metacercaria I actively ingests
materials from the host’s mantle. Furthermore, Stunkard and Uzmann
have stated : “ The yellow material (in caecal cells and lumen) appears
like that in the digestive gland of the clam and may be taken by the
parasite from the vascular fluid of the mollusk.”
19. Cercaria myae Uzmann, 1952. (Fig. 138)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
Cercaria myae was originally described by Uzmann (1952) from the
soft clam, Mya arenaria, collected in the vicinity of Newburyport,
Massachusetts. It has been subsequently found in the same host
collected at Boothbay Harbor, Maine (Stunkard and Uzmann, 1958),
and I (unpublished) have found it in the same clam in Narragansett
Bay, Rhode Island.
Description of stages in mollusc. Sporocyst motile, unpigmented,
clavate, occupying interfollicular spaces of gonad and interlobular
spaces of digestive gland of host, few throughout haemocoel, with thin
wall and birthpore at apical end; 0.21-0.60 mm long. Cercaria (Fig.
138) small, elongate ovoid, furcocercous ; body proper 0.12-0.25 mm
long ; tail stem short, about one-third body length, slightly shorter than
furcae ; body covered with minute spines, each 0.001 mm long ; delicate
setae on posterior surfaces of furcae ; anterior sucker 0.039-0-052 mm
in diameter ; ventral sucker 0-040-0.046 mm in diameter ; prepharynx
superfamily Fellodistomatoidea ; family Fellodistomatidae)