282
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
0. seminuda attached to C. fornicata from Bass River, an estuarine
habitat near West Dennis, Massachusetts. When these 0. seminuda
were detached from C. fornicata and given a choice between C. fornicata
and Crassostrea virginica, after 2 weeks, of the fifty-eight specimens of
0. seminuda tested, forty were found in the feeding position on C.
fornicata, their original host, and eighteen were wandering on the
substrate. I n a second experiment during which specimens of C.
virginica were placed between 0. seminuda and C. fornicata so that in
order to reach its original host, 0. seminuda had to by-pass the oysters,
it was found that after 2 days, of the thirty 0. seminuda tested, twentyfour were attached to C. fornicata and two to C. virginica. The remainder
were free on the substrate. From these and similar experiments, Boss
and Merrill have concluded that 0. seminuda prefers its original host,
C. fornicata, but will exchange hosts to some degree. Furthermore, it
has been determined that this parasitic gastropod does spend considerable time off of hosts.
In another series of experiments, Boss and Merrill (1965) have
demonstrated that if 0. seminuda is exposed to various hosts, including
Mercenaria mercenaria, Aequipecten irradians, Crepidula fornicata,
C. plana, Crucibulum striatum, Crassostrea virginica, Arctica (= Pecten)
islandica, Placopecten magellanicus and Modiolus modiolus, it prefers
C. fornicata but will become attached in varying numbers to all of the
other molluscs except A. islandica and C. plana. Furthermore, it
shows some preferential behavior towards A . irradians, C. striatum
and M . modiolus, especially if C. fornicata is not available.
Pathology. Although nothing is known about the effects of Odostomia
seminuda on the commercially important species of molluscs which it
is known to parasitize, Merrill and Boss (1964) have examined the
effects of this parasite on Crepidula fornicata and Crucibulum striatum.
It has been noted that the parasite’s proboscis actually penetrates the
host’s mantle and in some instances it actually pierces the visceral
mass. The host responds to this penetration by muscular contraction
in the immediate area. In the same paper, Merrill and Boss have
pointed out that 0. seminuda only feeds intermittently on its host.
4. Odostomia scalaris Mcgillivray, 1843. (Fig. 185)
(Class Gastropoda; subclass Opisthobranchia; order Tectibranchia; family
Odostomia scalaris has been found by Ankel and Christensen (1963)
feeding on the prosobranchs Hydrobia ulvae, Lacuna divaricata,
Littorina saxatilis and Rissoa membranacea, and on the scallop Chlamys
opercularis in Danish waters. Earlier, Pelseneer (1914) and others
Pyramidellidae)
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
0. seminuda attached to C. fornicata from Bass River, an estuarine
habitat near West Dennis, Massachusetts. When these 0. seminuda
were detached from C. fornicata and given a choice between C. fornicata
and Crassostrea virginica, after 2 weeks, of the fifty-eight specimens of
0. seminuda tested, forty were found in the feeding position on C.
fornicata, their original host, and eighteen were wandering on the
substrate. I n a second experiment during which specimens of C.
virginica were placed between 0. seminuda and C. fornicata so that in
order to reach its original host, 0. seminuda had to by-pass the oysters,
it was found that after 2 days, of the thirty 0. seminuda tested, twentyfour were attached to C. fornicata and two to C. virginica. The remainder
were free on the substrate. From these and similar experiments, Boss
and Merrill have concluded that 0. seminuda prefers its original host,
C. fornicata, but will exchange hosts to some degree. Furthermore, it
has been determined that this parasitic gastropod does spend considerable time off of hosts.
In another series of experiments, Boss and Merrill (1965) have
demonstrated that if 0. seminuda is exposed to various hosts, including
Mercenaria mercenaria, Aequipecten irradians, Crepidula fornicata,
C. plana, Crucibulum striatum, Crassostrea virginica, Arctica (= Pecten)
islandica, Placopecten magellanicus and Modiolus modiolus, it prefers
C. fornicata but will become attached in varying numbers to all of the
other molluscs except A. islandica and C. plana. Furthermore, it
shows some preferential behavior towards A . irradians, C. striatum
and M . modiolus, especially if C. fornicata is not available.
Pathology. Although nothing is known about the effects of Odostomia
seminuda on the commercially important species of molluscs which it
is known to parasitize, Merrill and Boss (1964) have examined the
effects of this parasite on Crepidula fornicata and Crucibulum striatum.
It has been noted that the parasite’s proboscis actually penetrates the
host’s mantle and in some instances it actually pierces the visceral
mass. The host responds to this penetration by muscular contraction
in the immediate area. In the same paper, Merrill and Boss have
pointed out that 0. seminuda only feeds intermittently on its host.
4. Odostomia scalaris Mcgillivray, 1843. (Fig. 185)
(Class Gastropoda; subclass Opisthobranchia; order Tectibranchia; family
Odostomia scalaris has been found by Ankel and Christensen (1963)
feeding on the prosobranchs Hydrobia ulvae, Lacuna divaricata,
Littorina saxatilis and Rissoa membranacea, and on the scallop Chlamys
opercularis in Danish waters. Earlier, Pelseneer (1914) and others
Pyramidellidae)