252
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
boats ” in England. Its systematic position cannot be determined from
the available information.
Description of &yes in mollusc. Sporocyst (Fig. 163) long, 1.43.0 mm in length, sausage-shaped, pale yellow or colorless ; may contain
twenty to thirty cercariae. Cercaria (Fig. 164) 0.33 mm long including
tail ; tail, 0.06 mm long, elongate cup-shaped ; anterior sucker 0-046 mm
in transverse diameter ; stylet with four points a t anterior terminal of
body, with middle pair of points long and outer pair short and bluntly
rounded behind ; ventral sucker posterior to midlength of body, same
size as anterior sucker ; penetration glands (Lebour depicts two groups
of six) situated between suckers, close to ventral sucker ; three ducts
from each group of glands open to exterior in area of stylet: excretory
vesicle epitheloid and oval.
39. Cercaria tenuans sp. inq. Cole, 1935. (Figs. 165 and 166)
(Taxonomic position undetermined)
During 1933, Cole (1935) investigated an unusual mortality which
occurred among the mussels, Mytilus edulis, brought to Conway,
Wales, for purification. Among the 900-1 000 mussels which had died,
he examined 300-400 and found six to be infected by a larval trematode.
Since the mantle of parasitized M . edulis revealed “ a vivid marigold
to blood orange ” color, Cole referred to the condition as the “ orange
sickness of mussels ”. Although the percentage of infection found by
Cole was not large, he stated:
That this parasite was much more prevalent in the early years of the
Conway installation seems certain, as Dr. Dodgson tells me that at one time
it was possible to obtain specimens by inspecting the few dead mussels which
are picked out of the tanks during the normal process of purification.
Cole also mentioned that Atkins (1931) had found but did not describe
this parasite in 2.16% of the mussels she had examined from Padstow,
Devon.
Description of stages in mollusc. Sporocysts (Fig. 165) in all tissues of
host’s body, particularly mantle, but not in foot; bright orange and
thin-walled, oval, moderately contractile, vary considerably in size ;
those containing fully developed and active cercariae averaging 1.1 mm
X 0.45 mm; orange pigment spotty, rest of sporocyst wall colorless;
thickened grayish rim at anterior end. Cercaria (Fig. 166) 0.3 mm
when fully extended ; without tail ; anterior sucker 0.05 mm in diameter ;
ventral sucker 0-07 mm in diameter, with its center being 0-18 mm
from anterior body terminal ; pharynx present, esophagus non-existent
or extremely short ; intestinal caeca short and bulbous, terminating in
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
boats ” in England. Its systematic position cannot be determined from
the available information.
Description of &yes in mollusc. Sporocyst (Fig. 163) long, 1.43.0 mm in length, sausage-shaped, pale yellow or colorless ; may contain
twenty to thirty cercariae. Cercaria (Fig. 164) 0.33 mm long including
tail ; tail, 0.06 mm long, elongate cup-shaped ; anterior sucker 0-046 mm
in transverse diameter ; stylet with four points a t anterior terminal of
body, with middle pair of points long and outer pair short and bluntly
rounded behind ; ventral sucker posterior to midlength of body, same
size as anterior sucker ; penetration glands (Lebour depicts two groups
of six) situated between suckers, close to ventral sucker ; three ducts
from each group of glands open to exterior in area of stylet: excretory
vesicle epitheloid and oval.
39. Cercaria tenuans sp. inq. Cole, 1935. (Figs. 165 and 166)
(Taxonomic position undetermined)
During 1933, Cole (1935) investigated an unusual mortality which
occurred among the mussels, Mytilus edulis, brought to Conway,
Wales, for purification. Among the 900-1 000 mussels which had died,
he examined 300-400 and found six to be infected by a larval trematode.
Since the mantle of parasitized M . edulis revealed “ a vivid marigold
to blood orange ” color, Cole referred to the condition as the “ orange
sickness of mussels ”. Although the percentage of infection found by
Cole was not large, he stated:
That this parasite was much more prevalent in the early years of the
Conway installation seems certain, as Dr. Dodgson tells me that at one time
it was possible to obtain specimens by inspecting the few dead mussels which
are picked out of the tanks during the normal process of purification.
Cole also mentioned that Atkins (1931) had found but did not describe
this parasite in 2.16% of the mussels she had examined from Padstow,
Devon.
Description of stages in mollusc. Sporocysts (Fig. 165) in all tissues of
host’s body, particularly mantle, but not in foot; bright orange and
thin-walled, oval, moderately contractile, vary considerably in size ;
those containing fully developed and active cercariae averaging 1.1 mm
X 0.45 mm; orange pigment spotty, rest of sporocyst wall colorless;
thickened grayish rim at anterior end. Cercaria (Fig. 166) 0.3 mm
when fully extended ; without tail ; anterior sucker 0.05 mm in diameter ;
ventral sucker 0-07 mm in diameter, with its center being 0-18 mm
from anterior body terminal ; pharynx present, esophagus non-existent
or extremely short ; intestinal caeca short and bulbous, terminating in