80
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Dermocystidium marinum. Similarly, increased numbers of ‘‘ brown
cells ” have been observed in Crassostrea virginica parasitized by MSX,
certain nematodes (unpublished), and Bucephalus sp. (Cheng and
Burton, 1965b). Recently Pauley and Sparks (1966) have reported the
occurrence of similar cells, although vacuolated and with as many as
three or four nuclei, in Crassostrea gigas experimentally injected with
turpentine.
Chemically, the smaller and larger “ brown cells ” have been shown
by Cheng and Burton (1966) not to include acid mucopolysaccharides
but the medium-sized ones, i.e. those that measure between 0.006 and
0.012 mm in diameter in C. virginica, are partially or totally positive for
acid mucopolysaccharide.
Moreover, slight metachromasia and
sphingomyelin are also found in certain “ brown cells ” of parasitized
oysters.
3. Nutritional requirements
If a symbiont, in this case primarily a parasite, is successful in
overcoming the initial or delayed confrontation with the host’s resistance, successful establishment may then proceed. Success now is
primarily dependent upon the parasite’s ability to cope with the host’s
relative susceptibility or partial insusceptibility. By Read’s ( 1958b)
definition stated earlier, a totally insusceptible host is one in which the
parasite’s life needs cannot be satisfied and therefore successful
establishment cannot occur. Information pertaining to the needs of
zooparasites of molluscs is conspicuously scanty. This is especially
true in the case of marine molluscs. As the result of the lack of information pertaining to the metabolism, particularly intermediary metabolism, of intramolluscan parasites and mutualists, there is no way to
estimate what their enzymic, coenzymic, and specific nutritional
requirements are. Moreover, it is generally not known if special
metabolic modifications exist which reflect their adaptations t o a
symbiotic existence.
I n this section is reviewed the available information about the
nutritional requirements of intramolluscan symbionts. The nature of
such information by necessity limits the discussion to what is known
concerning the nutritional aspects of larval trematodes in molluscs.
Cheng (1963d) has reviewed what is known about the biochemical
composition and requirements of intramolluscan trematode larvae.
Since then, a few additional facts of this nature pertaining to marine
molluscs have been contributed. Again, to make the review presented
below more meaningful, the general area of mollusc-parasite interactions as related to nutritional requirements must be consulted.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Dermocystidium marinum. Similarly, increased numbers of ‘‘ brown
cells ” have been observed in Crassostrea virginica parasitized by MSX,
certain nematodes (unpublished), and Bucephalus sp. (Cheng and
Burton, 1965b). Recently Pauley and Sparks (1966) have reported the
occurrence of similar cells, although vacuolated and with as many as
three or four nuclei, in Crassostrea gigas experimentally injected with
turpentine.
Chemically, the smaller and larger “ brown cells ” have been shown
by Cheng and Burton (1966) not to include acid mucopolysaccharides
but the medium-sized ones, i.e. those that measure between 0.006 and
0.012 mm in diameter in C. virginica, are partially or totally positive for
acid mucopolysaccharide.
Moreover, slight metachromasia and
sphingomyelin are also found in certain “ brown cells ” of parasitized
oysters.
3. Nutritional requirements
If a symbiont, in this case primarily a parasite, is successful in
overcoming the initial or delayed confrontation with the host’s resistance, successful establishment may then proceed. Success now is
primarily dependent upon the parasite’s ability to cope with the host’s
relative susceptibility or partial insusceptibility. By Read’s ( 1958b)
definition stated earlier, a totally insusceptible host is one in which the
parasite’s life needs cannot be satisfied and therefore successful
establishment cannot occur. Information pertaining to the needs of
zooparasites of molluscs is conspicuously scanty. This is especially
true in the case of marine molluscs. As the result of the lack of information pertaining to the metabolism, particularly intermediary metabolism, of intramolluscan parasites and mutualists, there is no way to
estimate what their enzymic, coenzymic, and specific nutritional
requirements are. Moreover, it is generally not known if special
metabolic modifications exist which reflect their adaptations t o a
symbiotic existence.
I n this section is reviewed the available information about the
nutritional requirements of intramolluscan symbionts. The nature of
such information by necessity limits the discussion to what is known
concerning the nutritional aspects of larval trematodes in molluscs.
Cheng (1963d) has reviewed what is known about the biochemical
composition and requirements of intramolluscan trematode larvae.
Since then, a few additional facts of this nature pertaining to marine
molluscs have been contributed. Again, to make the review presented
below more meaningful, the general area of mollusc-parasite interactions as related to nutritional requirements must be consulted.