14
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Philophthalmus, such as P. lucipetus, found in gulls in Europe,
P. skrjabini found in gulls in Russia and P. lachrymosus found in gulls
in Brazil. These, like P. hegneri in the United States, undergo larval
development in marine snails. In the case of P. hegneri, Penner and
Fried (1961, 1963) have reported that the molluscan intermediate host
is the marine snail BatilEaria minima found along the Gulf of Mexico
from Dunedin to Key West, Florida. Cercariae escaping from parasitized snails encyst ectopically and develop into metacercariae.
When these metacercariae are fed to certain birds, migration to the
eyes occurs and mature trematodes can be recovered from under the
nictitating membrane. Although Philophthalmus hegneri, P. lucipetus
and P. skrjabini have not been reported from mammals, P. lachrymosus
has (Dissanaike and Bilimoria, 1958). Furthermore, another related
freshwater species, P. gralli, has been shown experimentally to be able
to infect rabbits and white rats if cercariae or excysted metacercariae
were placed in their eyes (Alicata and Ching, 1960). According to these
authors : I‘ These results indicate possible methods of human infection
as reported in the literature.” It is thus possible that individuals
bathing in Philophthalmus-infested waters could become infected if
cercariae enter the eyes.
Philophthalmus is an example of a marine trematode of potential
public health importance. Since this area of parasitology, i.e. the
potential importance of marine parasites developing in molluscs, has
received practically no attention up until now, it is not onIy conceivable,
but very possible, that other zoonotic parasites of marine origin will be
found. With the world looking increasingly more to the ocean for
food substances, medical or public health marine parasitology will
undoubtedly receive increased attention.
111. IMPORTANCE TO BIOLOGY
A thorough understanding of relationships between symbionts and
marine molluscs can aid in answering various questions fundamental
to biology and a t the same time serve to resolve many of the problems
of the fisheries biologist and public health worker. By analyzing these
associations, it is possible to seek and obtain answers to such questions
as these. Are symbionts attracted to their hosts, and, if so, what are
the attracting forces! What are the nutritional requirements of
symbiotic protozoa, mesozoa, helminths, molluscs, annelids, arthropods
and other categories of symbionts, and what are the sources of these
requirements? Do differences exist between aspects of the metabolism
of ectophoretic and endoparasitic symbionts, and, if so, do these differences suggest mechanisms involved in the adaptation to endopara-
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Philophthalmus, such as P. lucipetus, found in gulls in Europe,
P. skrjabini found in gulls in Russia and P. lachrymosus found in gulls
in Brazil. These, like P. hegneri in the United States, undergo larval
development in marine snails. In the case of P. hegneri, Penner and
Fried (1961, 1963) have reported that the molluscan intermediate host
is the marine snail BatilEaria minima found along the Gulf of Mexico
from Dunedin to Key West, Florida. Cercariae escaping from parasitized snails encyst ectopically and develop into metacercariae.
When these metacercariae are fed to certain birds, migration to the
eyes occurs and mature trematodes can be recovered from under the
nictitating membrane. Although Philophthalmus hegneri, P. lucipetus
and P. skrjabini have not been reported from mammals, P. lachrymosus
has (Dissanaike and Bilimoria, 1958). Furthermore, another related
freshwater species, P. gralli, has been shown experimentally to be able
to infect rabbits and white rats if cercariae or excysted metacercariae
were placed in their eyes (Alicata and Ching, 1960). According to these
authors : I‘ These results indicate possible methods of human infection
as reported in the literature.” It is thus possible that individuals
bathing in Philophthalmus-infested waters could become infected if
cercariae enter the eyes.
Philophthalmus is an example of a marine trematode of potential
public health importance. Since this area of parasitology, i.e. the
potential importance of marine parasites developing in molluscs, has
received practically no attention up until now, it is not onIy conceivable,
but very possible, that other zoonotic parasites of marine origin will be
found. With the world looking increasingly more to the ocean for
food substances, medical or public health marine parasitology will
undoubtedly receive increased attention.
111. IMPORTANCE TO BIOLOGY
A thorough understanding of relationships between symbionts and
marine molluscs can aid in answering various questions fundamental
to biology and a t the same time serve to resolve many of the problems
of the fisheries biologist and public health worker. By analyzing these
associations, it is possible to seek and obtain answers to such questions
as these. Are symbionts attracted to their hosts, and, if so, what are
the attracting forces! What are the nutritional requirements of
symbiotic protozoa, mesozoa, helminths, molluscs, annelids, arthropods
and other categories of symbionts, and what are the sources of these
requirements? Do differences exist between aspects of the metabolism
of ectophoretic and endoparasitic symbionts, and, if so, do these differences suggest mechanisms involved in the adaptation to endopara-