124
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Rees has found no transitional stages from male to female or vice
versa he did suggest that there is the possibility of sex-reversal, since
among the individuals recovering from parasitization all were found
to be females while among the older non-parasitized snails there was
only a slight preponderance of females. As to whether this indirect
evidence is reliable is discussed below in connection with the preference
of host sex by larval trematodes.
Rothschild (1938) has also studied manifestations of gonadal
destruction in Hydrobia ulvae. She has found that the penes of all
infected snails are abnormal, usually more or less reduced in size. She
believed that some specimens without a penis are caused by the complete destruction of the testes. In one infected female, she found a
small penis ; however, she has stated that it is highly improbable that
all the infected snails with reduced penes are sex-reversed females.
From the above, it is concluded that true sex reversal in molluscs
caused by trematodes has yet to be convincingly demonstrated.
Krull’s findings, which have been confirmed by Rothschild, clearly
indicate that females whose ovaries are completely or mostly destroyed
could develop a small non-functional penis but these individuals have
not been shown ever to function as males. The only direct evidence is
that of Wesenberg-Lund (1931) ; however, it should be recalled that
Succinea putris is a hermaphroditic snail, hence the spermatozoa
observed by him may well represent gametes produced by the still
functional testicular tissues. His concept that a hermaphrodite can be
altered into a male can hardly be considered as true sex reversal.
Moreover, it should be recalled that Cheng and Cooperman (1964)
have demonstrated in Helisoma trivolvis parasitized by Glypthelmins
pennsylvaniensis that the parasites prefer the female reproductive
tract, thus sperm in the male tract may remain undamaged for some
time. It should also be mentioned that Laviolette (1954, 1956) has
shown in various arionid and limacid molluscs that castration of young
animals is followed by regeneration of the gonad and thus no secondary
effects are noticed. This information may be of importance in considering alterations of secondary sex organs in molluscs that are
temporarily parasitized during youth.
Other effects. Still other yet unexplained or partially explained
pathological changes in parasitized molluscs are known. WesenburgLund (1934) has reported that parasitized Lymnaea auriculata are often
thinner and corroded and certain whorls of their shells are “ ballooned”.
There are also color changes. On the other hand, Etges (1961) has
reported that specimens of Helisoma anceps parasitized by the rediae of
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Rees has found no transitional stages from male to female or vice
versa he did suggest that there is the possibility of sex-reversal, since
among the individuals recovering from parasitization all were found
to be females while among the older non-parasitized snails there was
only a slight preponderance of females. As to whether this indirect
evidence is reliable is discussed below in connection with the preference
of host sex by larval trematodes.
Rothschild (1938) has also studied manifestations of gonadal
destruction in Hydrobia ulvae. She has found that the penes of all
infected snails are abnormal, usually more or less reduced in size. She
believed that some specimens without a penis are caused by the complete destruction of the testes. In one infected female, she found a
small penis ; however, she has stated that it is highly improbable that
all the infected snails with reduced penes are sex-reversed females.
From the above, it is concluded that true sex reversal in molluscs
caused by trematodes has yet to be convincingly demonstrated.
Krull’s findings, which have been confirmed by Rothschild, clearly
indicate that females whose ovaries are completely or mostly destroyed
could develop a small non-functional penis but these individuals have
not been shown ever to function as males. The only direct evidence is
that of Wesenberg-Lund (1931) ; however, it should be recalled that
Succinea putris is a hermaphroditic snail, hence the spermatozoa
observed by him may well represent gametes produced by the still
functional testicular tissues. His concept that a hermaphrodite can be
altered into a male can hardly be considered as true sex reversal.
Moreover, it should be recalled that Cheng and Cooperman (1964)
have demonstrated in Helisoma trivolvis parasitized by Glypthelmins
pennsylvaniensis that the parasites prefer the female reproductive
tract, thus sperm in the male tract may remain undamaged for some
time. It should also be mentioned that Laviolette (1954, 1956) has
shown in various arionid and limacid molluscs that castration of young
animals is followed by regeneration of the gonad and thus no secondary
effects are noticed. This information may be of importance in considering alterations of secondary sex organs in molluscs that are
temporarily parasitized during youth.
Other effects. Still other yet unexplained or partially explained
pathological changes in parasitized molluscs are known. WesenburgLund (1934) has reported that parasitized Lymnaea auriculata are often
thinner and corroded and certain whorls of their shells are “ ballooned”.
There are also color changes. On the other hand, Etges (1961) has
reported that specimens of Helisoma anceps parasitized by the rediae of