162
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
facientis, is a pathogenic parasite found in the digestive gland and
nephridia of Mytilus californianus. It is of considerable interest since
it is the only known protozoan parasite of marine molluscs which
causes conspicuous swellings in the parasitized tissues.
1. Minchinia costalis (Wood and Andrews, 1962). (Figs. 53 and 54)
(Class Haplosporea ; order Haplosporida; family Haplosporidiidae)
During 1959-61, while studying the mortality of Crassostrea
virginica along the Virginia coast, Wood and Andrews (1962) discovered
a sporozoan parasite which they believed to be the cause of an oyster
disease that may lead to death. This parasite was originally referred
to as SSO (seaside organism) at informal conferences. In 1962, Wood
and Andrews formally described it as Haplosporidium costale. Later,
Sprague (1963), as the result of a revision of the genus Haplosporidiurn,
restored the genus Minchinia, which was originally erected by Labbe
in 1896 and later suppressed by Debaisieux in 1919, and placed H .
costale therein as M . costalis.
The genus Minchinia includes four other species that parasitize
molluscs. M . chitonis, originally named Klossia chitonis by Lankester
( 1885), later transferred to the genus Haplosporidium by Debaisieux
(1919), but considered the genotype of Minchinia by Labbe (1896)
and Sprague (1963), is a liver parasite of various European chitons ; M .
dentali, originally named Haplosporidium dentali by Arvy (1949), is
found in the scaphopod Dentalium ; M . piclcfordae, originally named
Haplosporidium piclcfordae by Barrow (1961), is found in the hepatopancreas of freshwater snails of the genera Helisoma, Physa and
Lymnaea in North America; and M . nelsoni is a parasite of the oyster,
Crassostrea virginica.
According to Sprague, Minchinia spores possess " a relatively
small orifice in the typically rounded anterior end but differ conspicuously in having a lid over the orifice " (Fig. 53). Furthermore,
he has stated that :
The lid is not homologous with that of Haplosporidiurn; it originates from
the outer gelatinous spore envelope instead of being a portion of the spore
membrane. Because of its separate origin, the lid lies over the orifice, not
in it, and has a free margin extending beyond the orifice and overlapping
the end of the spore.
Description of stages in mollusc. Parasitic in connective tissues of
Crassostrea virginica. Plasmodia in connective tissue, each measuring
6.1 x 7.8 p i n diameter (Fig. 54) ; spores obovate, truncate, uninucleate,
with operculum like that described by Sprague (1963) (Fig. 53) ; each
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
facientis, is a pathogenic parasite found in the digestive gland and
nephridia of Mytilus californianus. It is of considerable interest since
it is the only known protozoan parasite of marine molluscs which
causes conspicuous swellings in the parasitized tissues.
1. Minchinia costalis (Wood and Andrews, 1962). (Figs. 53 and 54)
(Class Haplosporea ; order Haplosporida; family Haplosporidiidae)
During 1959-61, while studying the mortality of Crassostrea
virginica along the Virginia coast, Wood and Andrews (1962) discovered
a sporozoan parasite which they believed to be the cause of an oyster
disease that may lead to death. This parasite was originally referred
to as SSO (seaside organism) at informal conferences. In 1962, Wood
and Andrews formally described it as Haplosporidium costale. Later,
Sprague (1963), as the result of a revision of the genus Haplosporidiurn,
restored the genus Minchinia, which was originally erected by Labbe
in 1896 and later suppressed by Debaisieux in 1919, and placed H .
costale therein as M . costalis.
The genus Minchinia includes four other species that parasitize
molluscs. M . chitonis, originally named Klossia chitonis by Lankester
( 1885), later transferred to the genus Haplosporidium by Debaisieux
(1919), but considered the genotype of Minchinia by Labbe (1896)
and Sprague (1963), is a liver parasite of various European chitons ; M .
dentali, originally named Haplosporidium dentali by Arvy (1949), is
found in the scaphopod Dentalium ; M . piclcfordae, originally named
Haplosporidium piclcfordae by Barrow (1961), is found in the hepatopancreas of freshwater snails of the genera Helisoma, Physa and
Lymnaea in North America; and M . nelsoni is a parasite of the oyster,
Crassostrea virginica.
According to Sprague, Minchinia spores possess " a relatively
small orifice in the typically rounded anterior end but differ conspicuously in having a lid over the orifice " (Fig. 53). Furthermore,
he has stated that :
The lid is not homologous with that of Haplosporidiurn; it originates from
the outer gelatinous spore envelope instead of being a portion of the spore
membrane. Because of its separate origin, the lid lies over the orifice, not
in it, and has a free margin extending beyond the orifice and overlapping
the end of the spore.
Description of stages in mollusc. Parasitic in connective tissues of
Crassostrea virginica. Plasmodia in connective tissue, each measuring
6.1 x 7.8 p i n diameter (Fig. 54) ; spores obovate, truncate, uninucleate,
with operculum like that described by Sprague (1963) (Fig. 53) ; each