5 . THE PHYLUM PROTOZOA
149
energy requirements of the adductor muscle under natural or artificial
conditions.
On the other hand, Landau and Galtsoff (1951), who have found this
parasite t o be widespread along the Atlantic and Gulf coasts of the United
States, have found no evidence to support the contention that N .
ostrearum is destructive to oysters. Similarly, Sprague and Orr (1955)
have found no evidence to indicate that N . ostrearum causes large scale
mortalities of oysters.
Rounded gymnospores, 3-4 p in
diameter, comprised of a group of sporozoites ; spores, formed when each
sporozoite secretes a resistant wall, each measures 10-16 p x 11-12 p,
generally found within phagocytes (Fig. 29); each spore encloses a
single sporozoite.
The complete life cycle of N . ostrearum has
been demonstrated by Prytherch (1938, 1940). This parasite utilizes
two hosts during its life cycle. The definitive host, according to
Prytherch (1940), Sprague (1950) and Kent (unpublished), is one of
four species of xanthid crabs, Panopeus herbsti, Eurypanopeus depressus,
Eurytium limosum or Neopanope texana. The crab becomes infected
when it ingests oyster leucocytes enclosing spores. This is generally
accomplished when infected oysters are ingested by the predatory
crab ; however, Feng (1958) has presented evidence that spore-enclosing
leucocytes may be discharged from oysters and these may serve as
the source of infection for crabs. When an ingested spore reaches the
crab’s intestine, the enclosed sporozoite emerges and becomes attached
to the gut wall by means of a small, globular epimerite and develops
into a motile sporadin (also known as a gregarine or trophozoite). The
next stage in its development involves the end-to-end coupling of a
number of sporadins. These soon break up and the young sporadins
again become fastened to the host’s intestinal wall. After a short
period of attachment and growth, the sporadins develop into short
cylindrical sporonts (LBger’s sporadins) which measure 18-30 p in
length. These sporonts become detached and actively migrate about the
intestinal lumen for 2-3 weeks during which they increase in size until
each one attains a length of 220-342 p. Some may penetrate through
the host’s gut epithelium.
As these sporonts approach maturity, two individuals of unequal
length become longitudinally attached in syzygy. Such a couple
becomes attached to the crab’s rectal wall and transforms into a gametocyst. Within the gametocyst the nucleus of each sporont, now
known as a gametocyte, undergoes repeated divisions followed by
Description of stages in mollusc.
Life cycle (Fig. 30).
149
energy requirements of the adductor muscle under natural or artificial
conditions.
On the other hand, Landau and Galtsoff (1951), who have found this
parasite t o be widespread along the Atlantic and Gulf coasts of the United
States, have found no evidence to support the contention that N .
ostrearum is destructive to oysters. Similarly, Sprague and Orr (1955)
have found no evidence to indicate that N . ostrearum causes large scale
mortalities of oysters.
Rounded gymnospores, 3-4 p in
diameter, comprised of a group of sporozoites ; spores, formed when each
sporozoite secretes a resistant wall, each measures 10-16 p x 11-12 p,
generally found within phagocytes (Fig. 29); each spore encloses a
single sporozoite.
The complete life cycle of N . ostrearum has
been demonstrated by Prytherch (1938, 1940). This parasite utilizes
two hosts during its life cycle. The definitive host, according to
Prytherch (1940), Sprague (1950) and Kent (unpublished), is one of
four species of xanthid crabs, Panopeus herbsti, Eurypanopeus depressus,
Eurytium limosum or Neopanope texana. The crab becomes infected
when it ingests oyster leucocytes enclosing spores. This is generally
accomplished when infected oysters are ingested by the predatory
crab ; however, Feng (1958) has presented evidence that spore-enclosing
leucocytes may be discharged from oysters and these may serve as
the source of infection for crabs. When an ingested spore reaches the
crab’s intestine, the enclosed sporozoite emerges and becomes attached
to the gut wall by means of a small, globular epimerite and develops
into a motile sporadin (also known as a gregarine or trophozoite). The
next stage in its development involves the end-to-end coupling of a
number of sporadins. These soon break up and the young sporadins
again become fastened to the host’s intestinal wall. After a short
period of attachment and growth, the sporadins develop into short
cylindrical sporonts (LBger’s sporadins) which measure 18-30 p in
length. These sporonts become detached and actively migrate about the
intestinal lumen for 2-3 weeks during which they increase in size until
each one attains a length of 220-342 p. Some may penetrate through
the host’s gut epithelium.
As these sporonts approach maturity, two individuals of unequal
length become longitudinally attached in syzygy. Such a couple
becomes attached to the crab’s rectal wall and transforms into a gametocyst. Within the gametocyst the nucleus of each sporont, now
known as a gametocyte, undergoes repeated divisions followed by
Description of stages in mollusc.
Life cycle (Fig. 30).