156
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Ecology. N . legeri is widely distributed in both northern and southern
Europe (Hatt, 1931). Nothing is known about the physiological aspects
of its ecology.
Pathology. Hatt (1931) has reviewed and contributed some new
information concerning histopathological changes in molluscs, primarily
pelecypods, parasitized by N . legeri. From what is known, there appears
to be little damage associated with this parasite. There is the formation
of minor lesions on the surfaces of gill lamellae during the penetration
process of gymnospores (Figs. 39 and 40) which may or may not involve
the complete destruction of cells in the immediate area or the sloughing
of cilia. The gymnospores, as a rule, enter via the intercellular spaces.
There is little or no host cellular reaction to gymnospores that have
entered regions of the host’s body which are packed with connective
tissues.
4. Porospora gigantea (van Beneden, 1869). (Figs. 41-46)
(6 ubclass Gregarinia; order Eugregarinia; suborder Cephalina; family
Porosporidae)
Porospora gigantea was the first porosporid gregarine to be described.
It was found by van Beneden (1869) in the intestine of a lobster and
named Gregarina gigantea. I n a series of subsequent papers (van
Beneden, 1871, 1872a,b) he has described the various stages in its
life history. It was later placed in the genus Porospora by Schneider
(1875). P. gigantea, like the other members of this genus, differs from
the members of the closely related genus Nematopsis by the fact that
its sporozoites are found in molluscan phagocytes without a protective
spore wall (Hatt, 1931).
Gymnospores spherical, 8 p in
diameter, comprised of approximately 1 5 0 0 merozoites (Figs. 41 and
42) ; naked sporozoites 17 p long (Figs. 43 and 44)) usually grouped
within phagocytes.
Life cycle. The life cycle of P. gigantea is essentially the same as
that of members of the genus Nematopsis (see Hatt, 1931). Two hosts
are involved, a crustacean definitive host, Homarus gammarus, and a
molluscan intermediate host, either Mytilus minimus or Trochocochlea
mutabilis. The sporadins, found in the gut of Homarus gummarus,
measure up to 10 mm long (Fig. 45). The gametocysts, found in the
lobster’s rectal region, measure from 3 to 4 mm in diameter.
The gymnospores invade the molluscan host via the intercellular
spaces of the gill filaments (Fig. 46). It is while in the process of working
its way through the gill surface that the gymnospores become phagocytized by the mollusc’s blood cells. It is still not completely underDescription of stages in mollusc.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Ecology. N . legeri is widely distributed in both northern and southern
Europe (Hatt, 1931). Nothing is known about the physiological aspects
of its ecology.
Pathology. Hatt (1931) has reviewed and contributed some new
information concerning histopathological changes in molluscs, primarily
pelecypods, parasitized by N . legeri. From what is known, there appears
to be little damage associated with this parasite. There is the formation
of minor lesions on the surfaces of gill lamellae during the penetration
process of gymnospores (Figs. 39 and 40) which may or may not involve
the complete destruction of cells in the immediate area or the sloughing
of cilia. The gymnospores, as a rule, enter via the intercellular spaces.
There is little or no host cellular reaction to gymnospores that have
entered regions of the host’s body which are packed with connective
tissues.
4. Porospora gigantea (van Beneden, 1869). (Figs. 41-46)
(6 ubclass Gregarinia; order Eugregarinia; suborder Cephalina; family
Porosporidae)
Porospora gigantea was the first porosporid gregarine to be described.
It was found by van Beneden (1869) in the intestine of a lobster and
named Gregarina gigantea. I n a series of subsequent papers (van
Beneden, 1871, 1872a,b) he has described the various stages in its
life history. It was later placed in the genus Porospora by Schneider
(1875). P. gigantea, like the other members of this genus, differs from
the members of the closely related genus Nematopsis by the fact that
its sporozoites are found in molluscan phagocytes without a protective
spore wall (Hatt, 1931).
Gymnospores spherical, 8 p in
diameter, comprised of approximately 1 5 0 0 merozoites (Figs. 41 and
42) ; naked sporozoites 17 p long (Figs. 43 and 44)) usually grouped
within phagocytes.
Life cycle. The life cycle of P. gigantea is essentially the same as
that of members of the genus Nematopsis (see Hatt, 1931). Two hosts
are involved, a crustacean definitive host, Homarus gammarus, and a
molluscan intermediate host, either Mytilus minimus or Trochocochlea
mutabilis. The sporadins, found in the gut of Homarus gummarus,
measure up to 10 mm long (Fig. 45). The gametocysts, found in the
lobster’s rectal region, measure from 3 to 4 mm in diameter.
The gymnospores invade the molluscan host via the intercellular
spaces of the gill filaments (Fig. 46). It is while in the process of working
its way through the gill surface that the gymnospores become phagocytized by the mollusc’s blood cells. It is still not completely underDescription of stages in mollusc.