62
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
intracellularly in phagocytes or removed through epithelial layers.
Later, Tripp (1961b), exploring the existence of these phenomena in
the only gastropod studied to date, Australorbis glabratus, introduced
by injection or implantation, yeast cells, bacteria, chicken erythrocytes,
carmine particles, willow pollen, polystyrene spheres, and homologous
and heterologous tissue implants into the cephalopedal sinus of the
snail. He reported that particles small enough to be phagocytized are
removed from the tissues by migration of host amoebocytes to the
exterior through epithelial layers, by intracellular degradation if the
particles are digestible, or by retention within tissue phagocytes.
Particles too large to be phagocytized (pollen and polystyrene spheres)
are enca-psulated in walls of fibroblasts. I n the case of tissue implants,
fresh homologous tissues elicit no response, fixed homologous tissues
are encapsulated, and fresh heterologous tissues are a t first also encapsulated but progressive atrophy of cells ensues and after 26 days
only a poorly organized fibrotic mass remains. The implant was by
then only surrounded by scattered groups of fibroblasts and the implant
tissue itself becomes invaded by fibroblasts and muscle cells which had
migrated from adjacent host connective tissues.
Other instances of phagocytosis in molluscs are known as the result
of histopathological studies. I n brief, Mackin (1951) has reported
phagocytosis of Dermocystidium marinum, a fungal parasite of oysters ;
Mackin et al. (1952) have reported phagocytosis of the flagellate
Hexamita by oyster leucocytes ; and Haskin (personal communication)
has found phagocytized MSX, now known as Ninchinia nelsoni, a
parasite of Crassostrea virginica which is believed to be the major
mortality factor among oysters along the mid-Atlantic coast of the
United States. The fates of these phagocytized parasites are not
known. I n addition to these observations, Mikhailova and Prazdnikov
(1961, 1962) have noted the occurrence of phagocytosis as an internal
defense mechanism against invading materials in Mytilus edulis.
Bang (1961) has contributed an interesting study of the mechanics
of phagocytosis by studying C. virginica leucocytes in vitro using both
phase-contrast and electron microscopy. By placing various freshly
grown marine bacteria in a drop of freshly obtained oyster blood, he
observed the process of phagocytosis. He discovered that although
phagocytosis of marine bacteria is readily demonstrable in most
instances, it is by no means an invariable phenomenon. When it occurs,
actual phagocytosis is usually preceded by a massive sticking of the
bacteria to the amoebocyte so that the amoebocyte resembled a
porcupine ”. This is followed by migration where the bacteria become
trapped between the fine filamentous pseudopods of the amoebocyte
‘<
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
intracellularly in phagocytes or removed through epithelial layers.
Later, Tripp (1961b), exploring the existence of these phenomena in
the only gastropod studied to date, Australorbis glabratus, introduced
by injection or implantation, yeast cells, bacteria, chicken erythrocytes,
carmine particles, willow pollen, polystyrene spheres, and homologous
and heterologous tissue implants into the cephalopedal sinus of the
snail. He reported that particles small enough to be phagocytized are
removed from the tissues by migration of host amoebocytes to the
exterior through epithelial layers, by intracellular degradation if the
particles are digestible, or by retention within tissue phagocytes.
Particles too large to be phagocytized (pollen and polystyrene spheres)
are enca-psulated in walls of fibroblasts. I n the case of tissue implants,
fresh homologous tissues elicit no response, fixed homologous tissues
are encapsulated, and fresh heterologous tissues are a t first also encapsulated but progressive atrophy of cells ensues and after 26 days
only a poorly organized fibrotic mass remains. The implant was by
then only surrounded by scattered groups of fibroblasts and the implant
tissue itself becomes invaded by fibroblasts and muscle cells which had
migrated from adjacent host connective tissues.
Other instances of phagocytosis in molluscs are known as the result
of histopathological studies. I n brief, Mackin (1951) has reported
phagocytosis of Dermocystidium marinum, a fungal parasite of oysters ;
Mackin et al. (1952) have reported phagocytosis of the flagellate
Hexamita by oyster leucocytes ; and Haskin (personal communication)
has found phagocytized MSX, now known as Ninchinia nelsoni, a
parasite of Crassostrea virginica which is believed to be the major
mortality factor among oysters along the mid-Atlantic coast of the
United States. The fates of these phagocytized parasites are not
known. I n addition to these observations, Mikhailova and Prazdnikov
(1961, 1962) have noted the occurrence of phagocytosis as an internal
defense mechanism against invading materials in Mytilus edulis.
Bang (1961) has contributed an interesting study of the mechanics
of phagocytosis by studying C. virginica leucocytes in vitro using both
phase-contrast and electron microscopy. By placing various freshly
grown marine bacteria in a drop of freshly obtained oyster blood, he
observed the process of phagocytosis. He discovered that although
phagocytosis of marine bacteria is readily demonstrable in most
instances, it is by no means an invariable phenomenon. When it occurs,
actual phagocytosis is usually preceded by a massive sticking of the
bacteria to the amoebocyte so that the amoebocyte resembled a
porcupine ”. This is followed by migration where the bacteria become
trapped between the fine filamentous pseudopods of the amoebocyte
‘<