4. ANALYSIS OF FACTORS INVOLVED IN SYMBIOSIS
53
during the initial attempt, subsequent trials are made until successful.
It has also been discovered that S. coccinea, which had settled on other
surfaces up to about 3 h earlier, transferred readily to M . modiolus
shells. During this process, the tent,acles and oral disk again make the
initial contacts with the shell, followed by release of the pedal disk from
the other surface and its attachment to the mussel shell. Anemones
which had settled on other surfaces for more than 3 h revealed no
tendency to transfer to shells.
Ross also has determined that the behavior is not specific for
M . modiolus. The shells of other pelecypods, including Pecten, will evoke
the same behavior. Furthermore, empty shells also will evoke the same
response. Ross considers this behavior as ‘‘ purposive ” and indicative
of preferential settling. Although the nature of the attraction remains
undetermined, the finding by Ross (1960) and Ross and Sutton (1961)
that the periostracum of Buccinum will attract Calliactis (Section I, C)
should be borne in mind.
F. Injlucnce of nature of substrate
In the case of those symbionts which can only arrive at their hosts
via migration across a solid or semi-solid substrate, the nature of the
substrate is often influential in determining the host-symbiont contact.
The results of Wikswo relative to the influence of glass versus sand as a
substrate for the migration of Arctonoe vittata has been cited in
Section I, C. In brief, she has found that the nature of the substrate
does influence the symbiont’s migration. Studies of this nature involving
marine molluscan hosts, or any mollusc for that matter, as far as I can
determine, are still wanting.
I n addition to influencing the symbiont’s migration towards its
host, the nature of the substrate may in some instances influence the
symbiont’s metamorphosis. This principle was first recognized by
Mortensen (1921) while working with echinoderms. He noticed that
metamorphosis may not always take place a t a fixed stage during
development and that the presence of certain factors in the environment, however, will stimulate larvae to metamorphose. Thus it follows
that in the case of certain symbionts the physical and chemical nature
of the substrate governs metamorphosis and thus indirectly governs the
successful contact with their hosts, since in most instances a specific
stage of development must be reached before the symbiont can establish
itself on or in its host. This has been convincingly demonstrated by
Bourdillon (1950) who studied the settling and metamorphosis of the
commensal mussel M o d i o l a k and its subsequent contact with its
53
during the initial attempt, subsequent trials are made until successful.
It has also been discovered that S. coccinea, which had settled on other
surfaces up to about 3 h earlier, transferred readily to M . modiolus
shells. During this process, the tent,acles and oral disk again make the
initial contacts with the shell, followed by release of the pedal disk from
the other surface and its attachment to the mussel shell. Anemones
which had settled on other surfaces for more than 3 h revealed no
tendency to transfer to shells.
Ross also has determined that the behavior is not specific for
M . modiolus. The shells of other pelecypods, including Pecten, will evoke
the same behavior. Furthermore, empty shells also will evoke the same
response. Ross considers this behavior as ‘‘ purposive ” and indicative
of preferential settling. Although the nature of the attraction remains
undetermined, the finding by Ross (1960) and Ross and Sutton (1961)
that the periostracum of Buccinum will attract Calliactis (Section I, C)
should be borne in mind.
F. Injlucnce of nature of substrate
In the case of those symbionts which can only arrive at their hosts
via migration across a solid or semi-solid substrate, the nature of the
substrate is often influential in determining the host-symbiont contact.
The results of Wikswo relative to the influence of glass versus sand as a
substrate for the migration of Arctonoe vittata has been cited in
Section I, C. In brief, she has found that the nature of the substrate
does influence the symbiont’s migration. Studies of this nature involving
marine molluscan hosts, or any mollusc for that matter, as far as I can
determine, are still wanting.
I n addition to influencing the symbiont’s migration towards its
host, the nature of the substrate may in some instances influence the
symbiont’s metamorphosis. This principle was first recognized by
Mortensen (1921) while working with echinoderms. He noticed that
metamorphosis may not always take place a t a fixed stage during
development and that the presence of certain factors in the environment, however, will stimulate larvae to metamorphose. Thus it follows
that in the case of certain symbionts the physical and chemical nature
of the substrate governs metamorphosis and thus indirectly governs the
successful contact with their hosts, since in most instances a specific
stage of development must be reached before the symbiont can establish
itself on or in its host. This has been convincingly demonstrated by
Bourdillon (1950) who studied the settling and metamorphosis of the
commensal mussel M o d i o l a k and its subsequent contact with its