118
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
ovarian follicles appear degenerate and most are no longer visible. The
appearance of the few remaining Leydig cells suggest physiological
degradation. The integrity of the ovarian lobes is completely disrupted.
Moreover, the majority of the remaining ova appear degenerate and
smaller, averaging 0.028 x 0.021 mm instead of the normal average
of 0.053 x 0-030 mm. This finding serves to confirm the earlier observation of W. J. Rees (1936a) that the ova of Littorina littorea parasitized
by Cercaria ubiquita are smaller. It is of interest to note at this point
that subsequent histochemical studies by Cheng and Burton (1966)
have revealed that the amount of stored glycogen in the ova of infected
oysters is markedly reduced. Whether this is the result of utilization
by surrounding sporocysts or due to starvation resulting from blockage
of the glucose-transporting blood vessels, as suggested by W. J. Rees
(1936a), remains undetermined. Resorption of ova, however, does
occur. There is no doubt that parasitic castration occurs in Crassostrea
virginica parasitized by Bucephalus sp.
Affected tissues in extremely heavily parasitized oysters are not
limited to the circumenteral connective tissue tunica, the digestive
gland, and the gonads. Young sporocyst branches, as determined by the
polarity of their parenchymal cells (Cheng, 1966b), do infiltrate the
matrices of the palps, gills and mantle. In addition, sporocysts are
found in blood vessels, suggesting that this is a possible route of tissue
infiltration, and in water tubes situated at the base of gill lamellae,
which undoubtedly serve as the avenues for the infiltration of the gills.
Most of the damage that occurs in the gills, palps and mantle appears to
be mechanical in nature, although reduction in stored carbohydrates
at these sites does occur (Cheng and Burton, 1966).
The species of Bucephalus studied by us in Rhode Island is different
from B. cuculus reported by McCrady (1873) and others farther south
along the Atlantic coast of North America. Furthermore, it appears to
be different from B. haimeanus commonly found in European oysters
and clams. According to Hopkins (1954a, 1957a), B. cuculus is also
different from B. haimeanus and not a synonym as has been suggested
by Tennent (1905, 1906, 1909), Dawes (1946) and Yamaguti (1958).
Unfortunately, detailed histopathological changes associated with both
B. cuculus and B. haimeanus have not yet been studied. In the case
of B. cuculus, however, McCrady (1873), Tennent (1906) and Hopkins
(1954a), as the result of gross observations, have all pointed out that
the sporocysts are concentrated primarily in the gonads, and only in
extremely heavy infections, resulting from prolific growth of the
sporocysts, do the digestive gland and other parts of the oyster's
anatomy become infiltrated. I have been able to confirm this in
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
ovarian follicles appear degenerate and most are no longer visible. The
appearance of the few remaining Leydig cells suggest physiological
degradation. The integrity of the ovarian lobes is completely disrupted.
Moreover, the majority of the remaining ova appear degenerate and
smaller, averaging 0.028 x 0.021 mm instead of the normal average
of 0.053 x 0-030 mm. This finding serves to confirm the earlier observation of W. J. Rees (1936a) that the ova of Littorina littorea parasitized
by Cercaria ubiquita are smaller. It is of interest to note at this point
that subsequent histochemical studies by Cheng and Burton (1966)
have revealed that the amount of stored glycogen in the ova of infected
oysters is markedly reduced. Whether this is the result of utilization
by surrounding sporocysts or due to starvation resulting from blockage
of the glucose-transporting blood vessels, as suggested by W. J. Rees
(1936a), remains undetermined. Resorption of ova, however, does
occur. There is no doubt that parasitic castration occurs in Crassostrea
virginica parasitized by Bucephalus sp.
Affected tissues in extremely heavily parasitized oysters are not
limited to the circumenteral connective tissue tunica, the digestive
gland, and the gonads. Young sporocyst branches, as determined by the
polarity of their parenchymal cells (Cheng, 1966b), do infiltrate the
matrices of the palps, gills and mantle. In addition, sporocysts are
found in blood vessels, suggesting that this is a possible route of tissue
infiltration, and in water tubes situated at the base of gill lamellae,
which undoubtedly serve as the avenues for the infiltration of the gills.
Most of the damage that occurs in the gills, palps and mantle appears to
be mechanical in nature, although reduction in stored carbohydrates
at these sites does occur (Cheng and Burton, 1966).
The species of Bucephalus studied by us in Rhode Island is different
from B. cuculus reported by McCrady (1873) and others farther south
along the Atlantic coast of North America. Furthermore, it appears to
be different from B. haimeanus commonly found in European oysters
and clams. According to Hopkins (1954a, 1957a), B. cuculus is also
different from B. haimeanus and not a synonym as has been suggested
by Tennent (1905, 1906, 1909), Dawes (1946) and Yamaguti (1958).
Unfortunately, detailed histopathological changes associated with both
B. cuculus and B. haimeanus have not yet been studied. In the case
of B. cuculus, however, McCrady (1873), Tennent (1906) and Hopkins
(1954a), as the result of gross observations, have all pointed out that
the sporocysts are concentrated primarily in the gonads, and only in
extremely heavy infections, resulting from prolific growth of the
sporocysts, do the digestive gland and other parts of the oyster's
anatomy become infiltrated. I have been able to confirm this in