5 . T H E PHYLUM PROTOZOA
165
Detailed histopathological and histochemical changes associated
with M . costalis infections have not yet been studied although Farley
(1965), who stained sections of infected oysters with a modification of
Ziehl-Neelsen’s carbol fuchsin stain, has reported that the spores
(sporoplasm) of M . costalis are acid fast.
2. Minchinia nelsoni. (Figs. 56 and 57)
(Class Haplosporea; order Haplosporida; family Haplosporiidae)*
It is generally agreed among those interested in parasites of commercially important molluscs that the organism originally referred to
as MSX (multinucleated sphere unknown) and now known as Minchinia
nelsoni is by far the most destructive of the known parasites and is
believed t o be the causative agent of the mass oyster mortalities which
began in the Delaware and Chesapeake Bays during 1957 and have been
continuing and spreading ever since (Haskin et al., 1965). Although
considerable information is known about the distribution, seasonal
fluctuations, and morphology of the intramolluscan stages of MSX,
such information for the most part has not appeared in published
form but has been circulated informally among oyster biologists in
the United States. As the result of this situation, I am forced to present
the following information without being able to cite the publications or
in most instances the investigators.
Multinucleated spherical stage
(plasmodium) found in gills, palps, suprabranchial chambers and
Leydig tissues of Crassostren virginica (Figs. 56, 57A-F) but may be
found in other sites as well. Each plasmodium, 4-30 p (occasionally as
large as 50 p ) in greatest diameter, includes variable numbers of nuclei
(one to more than sixty); each nucleus, 1.5-7.5 p in diameter, possesses
a distinct endosome resting against a thin but sharply defined nuclear
membrane; intranuclear bar in all except smallest nuclei?; nuclei
frequently lying in central cytoplasmic zone surrounded by a less
densely staining cytoplasmic zone (Fig. 57A-C). According to Haskin
et al. (1966), two types of nuclei are recognizeable: (1) small nuclei,
1.5-1.6 p in diameter, with densely staining “ caps ” (Fig. 57E),
found in plasmodia generally concentrated in and under epithelium of
gills, palps and epibranchial chambers of recently infected oysters;
Description of stages in mollusc.
* MSX was only tentatively assigned to the genus Minchinia as M . nelsoni by
Haskin et al. (1966), and therefore its assignment t o the Haplosporiidae of the Haplosporide is also tentative.
t The nuclear details are visible in both fresh preparations stained with 0.1% methylene blue and in sectioned materials fixed in Zenker’s or Davidson’s fluids and stainecl
with Harris’ or iron hematoxylin.
165
Detailed histopathological and histochemical changes associated
with M . costalis infections have not yet been studied although Farley
(1965), who stained sections of infected oysters with a modification of
Ziehl-Neelsen’s carbol fuchsin stain, has reported that the spores
(sporoplasm) of M . costalis are acid fast.
2. Minchinia nelsoni. (Figs. 56 and 57)
(Class Haplosporea; order Haplosporida; family Haplosporiidae)*
It is generally agreed among those interested in parasites of commercially important molluscs that the organism originally referred to
as MSX (multinucleated sphere unknown) and now known as Minchinia
nelsoni is by far the most destructive of the known parasites and is
believed t o be the causative agent of the mass oyster mortalities which
began in the Delaware and Chesapeake Bays during 1957 and have been
continuing and spreading ever since (Haskin et al., 1965). Although
considerable information is known about the distribution, seasonal
fluctuations, and morphology of the intramolluscan stages of MSX,
such information for the most part has not appeared in published
form but has been circulated informally among oyster biologists in
the United States. As the result of this situation, I am forced to present
the following information without being able to cite the publications or
in most instances the investigators.
Multinucleated spherical stage
(plasmodium) found in gills, palps, suprabranchial chambers and
Leydig tissues of Crassostren virginica (Figs. 56, 57A-F) but may be
found in other sites as well. Each plasmodium, 4-30 p (occasionally as
large as 50 p ) in greatest diameter, includes variable numbers of nuclei
(one to more than sixty); each nucleus, 1.5-7.5 p in diameter, possesses
a distinct endosome resting against a thin but sharply defined nuclear
membrane; intranuclear bar in all except smallest nuclei?; nuclei
frequently lying in central cytoplasmic zone surrounded by a less
densely staining cytoplasmic zone (Fig. 57A-C). According to Haskin
et al. (1966), two types of nuclei are recognizeable: (1) small nuclei,
1.5-1.6 p in diameter, with densely staining “ caps ” (Fig. 57E),
found in plasmodia generally concentrated in and under epithelium of
gills, palps and epibranchial chambers of recently infected oysters;
Description of stages in mollusc.
* MSX was only tentatively assigned to the genus Minchinia as M . nelsoni by
Haskin et al. (1966), and therefore its assignment t o the Haplosporiidae of the Haplosporide is also tentative.
t The nuclear details are visible in both fresh preparations stained with 0.1% methylene blue and in sectioned materials fixed in Zenker’s or Davidson’s fluids and stainecl
with Harris’ or iron hematoxylin.