4. ANALYSIS O F FACTORS INVOLVED I N SYMBIOSIS
127
pigment present in the hepatopancreas of Littorina littorea since
concentrated extracts of this pigment possess absorption peaks at
420, 450 and 660mp. Furthermore, as the result of comparing the
characteristics of this pigment with those of known pigments (Fox,
1953), the snail pigment has been identified as a carotenoid.
Willey and Gross have concluded that the pigment in the foot of
parasitized snails must be released through the destruction of hepatopancreatic cells and is conducted, probably via the circulation, to the
foot musculature.
In connection with the release of carotenoid pigments from molluscan
hepatopancreatic cells, James (1 965) has commented that their release
from histolyzed glands in the haemocoel may be an explanation for
gigantism rather than parasitic castration, since Deuel(l957) has shown
that some of the carotenoids are precursors of the growth-promoting
vitamin A.
It should be noted that at least two earlier workers, W. J. Rees and
F. G. Rees, have reported changes in the coloration of the hepatopancreas of parasitized marine molluscs. Both of them have noticed a
decrease in the amount of pigmentation in the glands of infected snails
except in the instances of infection by Himasthla leptosoma in which
case the parasitized gland becomes bright orange. This could mean
that the rediae concentrate the released pigments during their active
feeding and their presence in the gland gives the latter its bright orange
color. Pigments are not limited to rediae. Nadakal (1960a,b), who
studied the nature and origin of pigments found in ten species of
trematodes in the marine snail Cerithidea californica, has reported that
p-carotene is present in eight of these species. Furthermore, a ketocarotenoid has been identified from one of the species of sporocysts.
On the other hand, only three species of rediae and none of the sporocysts contain chlorophyll derivatives. Nadakal is of the opinion, and
probably correctly so, that the carotenoid and chlorophyllic pigments
are passed along to the snail via its food chain and the parasites absorb
these pigments from the snail host. He has also noted that there appears
to be selective absorption of only the hydrocarbons from several kinds
of carotenoids available in the snails. No significant metabolic alteration
of pigments in the trematode larvae has been found. Thus the intake of
pigments from the molluscan host can be accomplished by selective
absorption or, as in the case of Himasthla leptosoma rediae, most
probably by active ingestion.
Ewers and Rose (1965) have reported another interesting, although
still not completely understood, manifestation of parasitism in marine
gastropods. They have found that a small proportion of individuals of
127
pigment present in the hepatopancreas of Littorina littorea since
concentrated extracts of this pigment possess absorption peaks at
420, 450 and 660mp. Furthermore, as the result of comparing the
characteristics of this pigment with those of known pigments (Fox,
1953), the snail pigment has been identified as a carotenoid.
Willey and Gross have concluded that the pigment in the foot of
parasitized snails must be released through the destruction of hepatopancreatic cells and is conducted, probably via the circulation, to the
foot musculature.
In connection with the release of carotenoid pigments from molluscan
hepatopancreatic cells, James (1 965) has commented that their release
from histolyzed glands in the haemocoel may be an explanation for
gigantism rather than parasitic castration, since Deuel(l957) has shown
that some of the carotenoids are precursors of the growth-promoting
vitamin A.
It should be noted that at least two earlier workers, W. J. Rees and
F. G. Rees, have reported changes in the coloration of the hepatopancreas of parasitized marine molluscs. Both of them have noticed a
decrease in the amount of pigmentation in the glands of infected snails
except in the instances of infection by Himasthla leptosoma in which
case the parasitized gland becomes bright orange. This could mean
that the rediae concentrate the released pigments during their active
feeding and their presence in the gland gives the latter its bright orange
color. Pigments are not limited to rediae. Nadakal (1960a,b), who
studied the nature and origin of pigments found in ten species of
trematodes in the marine snail Cerithidea californica, has reported that
p-carotene is present in eight of these species. Furthermore, a ketocarotenoid has been identified from one of the species of sporocysts.
On the other hand, only three species of rediae and none of the sporocysts contain chlorophyll derivatives. Nadakal is of the opinion, and
probably correctly so, that the carotenoid and chlorophyllic pigments
are passed along to the snail via its food chain and the parasites absorb
these pigments from the snail host. He has also noted that there appears
to be selective absorption of only the hydrocarbons from several kinds
of carotenoids available in the snails. No significant metabolic alteration
of pigments in the trematode larvae has been found. Thus the intake of
pigments from the molluscan host can be accomplished by selective
absorption or, as in the case of Himasthla leptosoma rediae, most
probably by active ingestion.
Ewers and Rose (1965) have reported another interesting, although
still not completely understood, manifestation of parasitism in marine
gastropods. They have found that a small proportion of individuals of