86
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
In the case of rediae, as far as I can determine, Ginecinskij’s (1961)
report of the occurrence of lipids in the rediae of members of the
Echinostomatidae and Notocotylidae, embedded in the hepatopancreas
of their respective molluscan hosts, is the only one available.
The occurrence of lipids in cercariae has been more frequently
studied (Ivanov, 1950; Deiana, 1954a,b ; Ginecinskij, 1961 ; Ginecinskij
and Dobrovalskij, 1962; Lutta, 1939; Palm, 1962a,b; Cheng and
Snyder, 1962c ; Cheng, 196513). Lipids as a rule are found limited to the
excretory (osmoregulatory) system and to the parenchyma. Cheng and
Snyder (1962b), thus far the only ones to employ more specific and
differentiating histochemical tests, have pointed out that in Helisoma
trivolvis parasitized by Glypthelmins pennsylvaniensis there i s an
initial increase in the amount of neutral fats stored in the host’s
hepatopancreatic cells. The neutral fats, however, are gradually
degraded to fatty acids. Much of these short-chained fatty acids are
believed to pass through the wall of the sporocysts. This hypothesis is
based on the finding of fatty acid droplets adhering to the walls and in
the brood chambers of sporocysts. Concurrent with the loss of fatty
acids from host cells, leaving conspicuous cytoplasmic vacuoles in these
cells, there is the appearance of fatty acid deposits in older developing
cercariae. Cheng and Snyder have stated that it is not surprising that
fatty acids, rather than neutral fats, are found deposited in the body of
cercariae, basing this on the fact that it is generally the unsaturated
higher fatty acids, rather than fats, which are found in adult parasitic
platyhelminths. It was not until Cheng’s (1965b) later work with
Crassostrea virginica parasitized by Bucephalus sp. that neutral fats
were discovered in certain cells comprising older germ balls and in
developing cercariae as detected by the oil red 0 technique of Lillie
(1944). No explanation is yet possible as to why neutral fats, in
addition to fatty acids, are present in the intramolluscan larvae of this
parasite of a marine pelecypod. In addition to this difference, another
has also been reported. In parasitized oysters there is an increase in
total fats in the digestive diverticular (hepatopancreatic) cells. This,
upon further histochemical analysis, has been found to reflect increases
of both neutral fats and fatty acids. The increase in fatty acids is
believed to be due to hydrolysis of the neutral fats by lipase of parasite
origin. This enzyme was detected in cercarial tissues, in brood chambers,
and adhering to sporocyst walls. No explanation is yet available as to
why there is no subsequent decrease in fatty acids as in the case of
Helisoma trivolvis infected with Glypthelmins pennsylvaniensis. Moreover, no explanation is again yet available as to why the level of neutral
fats in the host’s cells increases in spite of their degradation by lipase
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
In the case of rediae, as far as I can determine, Ginecinskij’s (1961)
report of the occurrence of lipids in the rediae of members of the
Echinostomatidae and Notocotylidae, embedded in the hepatopancreas
of their respective molluscan hosts, is the only one available.
The occurrence of lipids in cercariae has been more frequently
studied (Ivanov, 1950; Deiana, 1954a,b ; Ginecinskij, 1961 ; Ginecinskij
and Dobrovalskij, 1962; Lutta, 1939; Palm, 1962a,b; Cheng and
Snyder, 1962c ; Cheng, 196513). Lipids as a rule are found limited to the
excretory (osmoregulatory) system and to the parenchyma. Cheng and
Snyder (1962b), thus far the only ones to employ more specific and
differentiating histochemical tests, have pointed out that in Helisoma
trivolvis parasitized by Glypthelmins pennsylvaniensis there i s an
initial increase in the amount of neutral fats stored in the host’s
hepatopancreatic cells. The neutral fats, however, are gradually
degraded to fatty acids. Much of these short-chained fatty acids are
believed to pass through the wall of the sporocysts. This hypothesis is
based on the finding of fatty acid droplets adhering to the walls and in
the brood chambers of sporocysts. Concurrent with the loss of fatty
acids from host cells, leaving conspicuous cytoplasmic vacuoles in these
cells, there is the appearance of fatty acid deposits in older developing
cercariae. Cheng and Snyder have stated that it is not surprising that
fatty acids, rather than neutral fats, are found deposited in the body of
cercariae, basing this on the fact that it is generally the unsaturated
higher fatty acids, rather than fats, which are found in adult parasitic
platyhelminths. It was not until Cheng’s (1965b) later work with
Crassostrea virginica parasitized by Bucephalus sp. that neutral fats
were discovered in certain cells comprising older germ balls and in
developing cercariae as detected by the oil red 0 technique of Lillie
(1944). No explanation is yet possible as to why neutral fats, in
addition to fatty acids, are present in the intramolluscan larvae of this
parasite of a marine pelecypod. In addition to this difference, another
has also been reported. In parasitized oysters there is an increase in
total fats in the digestive diverticular (hepatopancreatic) cells. This,
upon further histochemical analysis, has been found to reflect increases
of both neutral fats and fatty acids. The increase in fatty acids is
believed to be due to hydrolysis of the neutral fats by lipase of parasite
origin. This enzyme was detected in cercarial tissues, in brood chambers,
and adhering to sporocyst walls. No explanation is yet available as to
why there is no subsequent decrease in fatty acids as in the case of
Helisoma trivolvis infected with Glypthelmins pennsylvaniensis. Moreover, no explanation is again yet available as to why the level of neutral
fats in the host’s cells increases in spite of their degradation by lipase