88
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
bolism as an energy source occurs primarily during the post-molluscan,
free-swimming phases of the life-span of cercariae. Specifically,
Ginecinskij has found that stored lipids are completely exhausted during
the free-swimming phase of several species of cercariae, namely
Opisthioglyphae ranae, Cotylurus brevis and Cercaria spinulosa. I n other
species, namely Cercaria helvetica XXII and two unidentified xiphidiocercariae, the stored lipids are only slightly diminished.
It is of interest to point out that Ginecinskij has reported in the
same paper that there are practically no stored lipids in non-swimming
cercariae, small quantities in gliding furcocercous cercariae, and
relatively large quantities in active swimmers, thus suggesting a correlation between the degree of activity during the post-molluscan phase
and the amount of stored lipids. Ginecinskij has proposed to explain this
condition in terms of the type of cercarial motility. She postulated that
the stored lipids may play a hydrostatic role, i.e. in lightening the body
weight, since fatty droplets are absent in non-swimmers, present in
small amounts in gliders, and in relatively large quantities in active
swimmers. Perhaps her interpretation is justified and the lipids do
serve a dual function. However, in my opinion the correlation between
active swimming and the abundance of Iipids and their metabolic
utilization is the more important one.
c . Proteins
From the broad viewpoint, there can be no doubt that intramolluscan parasites, and perhaps mutualists, especially those embedded
in their hosts’ tissues, must derive some, if not all, of their proteins
and amino acid requirements from the host. Even among those
symbionts which live near or within the mantle cavity of such pelecypods as oysters, it is more than likely that they derive certain proteins
and amino acids from the host’s blood seeping into the mantle cavity.
Furthermore, some of these molecules may be released during diapedesis
which is a naturally occurring phenomenon among these molluscs
(Galtsoff, 1964).
Specific data pertaining to specific parasites are in most instances
wanting. Studies on amino acid uptake comparable to those of
Stephens (1962a,b, 1964) and Stephens and Schinske (1961) on freeliving estuarine invertebrates or on the amino acid compositions and
metabolism of molluscs (reviewed by Allen, 1961a) are not yet available
for organisms associated with marine molluscs. Evidences, however, are
available which suggest that trematode larvae in freshwater molluscs do
utilize free amino acids derived from their hosts’ adjacent tissues and
plasma (Cheng, 1963d). Such data may well have their counterparts
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
bolism as an energy source occurs primarily during the post-molluscan,
free-swimming phases of the life-span of cercariae. Specifically,
Ginecinskij has found that stored lipids are completely exhausted during
the free-swimming phase of several species of cercariae, namely
Opisthioglyphae ranae, Cotylurus brevis and Cercaria spinulosa. I n other
species, namely Cercaria helvetica XXII and two unidentified xiphidiocercariae, the stored lipids are only slightly diminished.
It is of interest to point out that Ginecinskij has reported in the
same paper that there are practically no stored lipids in non-swimming
cercariae, small quantities in gliding furcocercous cercariae, and
relatively large quantities in active swimmers, thus suggesting a correlation between the degree of activity during the post-molluscan phase
and the amount of stored lipids. Ginecinskij has proposed to explain this
condition in terms of the type of cercarial motility. She postulated that
the stored lipids may play a hydrostatic role, i.e. in lightening the body
weight, since fatty droplets are absent in non-swimmers, present in
small amounts in gliders, and in relatively large quantities in active
swimmers. Perhaps her interpretation is justified and the lipids do
serve a dual function. However, in my opinion the correlation between
active swimming and the abundance of Iipids and their metabolic
utilization is the more important one.
c . Proteins
From the broad viewpoint, there can be no doubt that intramolluscan parasites, and perhaps mutualists, especially those embedded
in their hosts’ tissues, must derive some, if not all, of their proteins
and amino acid requirements from the host. Even among those
symbionts which live near or within the mantle cavity of such pelecypods as oysters, it is more than likely that they derive certain proteins
and amino acids from the host’s blood seeping into the mantle cavity.
Furthermore, some of these molecules may be released during diapedesis
which is a naturally occurring phenomenon among these molluscs
(Galtsoff, 1964).
Specific data pertaining to specific parasites are in most instances
wanting. Studies on amino acid uptake comparable to those of
Stephens (1962a,b, 1964) and Stephens and Schinske (1961) on freeliving estuarine invertebrates or on the amino acid compositions and
metabolism of molluscs (reviewed by Allen, 1961a) are not yet available
for organisms associated with marine molluscs. Evidences, however, are
available which suggest that trematode larvae in freshwater molluscs do
utilize free amino acids derived from their hosts’ adjacent tissues and
plasma (Cheng, 1963d). Such data may well have their counterparts