5 . THE PHYLUM PROTOZOA
175
dextrose agar, nutrient agar, and thioglycollate agar. All his attempts
have been unsuccessful although mature spores maintained their jntegrity in these media for 3 months.
Pathology. H . tumefacientis causes tumefactions (swellings) in its
host’s tissues. These swellings vary in size and are light brown or tan
in color. Microscopically, parasites in the digestive gland tubules tend
to be subepithelial, situated towards the peripheral margin of each cell.
As they develop, they displace the epithelial cells and may inhibit
their growth. Despite these histopathological alterations, no necrosis
of mussel tissues or neoplasms occur. The fate of infected mussels is
not known.
E. Subphylum CNIDOSPORA
Class Microsporidea
The microsporidean genus Chytridiopsis includes two species known
to parasitize commercially important marine molluscs. These protozoa,
at one time considered to be sporozoans, are now considered to be
members of a distinct subphylum, the Cnidospora.
1. Chytridiopsis mytilovum (Field, 1924). (Figs. 66-76)
(Order Microsporida; family?)
Chytridiopsis mytilovum was originally superficially described by
Field (1924) who was making a comprehensive study of the host,
Mytilus edulis. Although he admitted little familiarity with the
Sporozoa,” he felt obliged to report the occurrence of this parasite in
the ova of the mussel. He stated that: “ It was finally identified for
the author through the kindness of Dr. Gary N. Calkins, of Columbia
University, as a probably new species of the genus Haplosporidium.”
As the result, Field briefly described the parasite, namedit H . rnytilovum,
and promised to investigate it further. Unfortunately, he died soon
thereafter and no additional studies were made.
Sprague rediscovered H . mytilovum in the ova of the same host,
Mytilus edulis, collected at Ocean City, Maryland. After critical study,
he (Sprague, 1963) stated that it does not belong to the genus Haplosporidium and later (Sprague, 1965a) transferred it to Chytridiopsis, a
genus the systematic position of which remains uncertain. I n his
discussion, Sprague pointed out that Chytridiopsis has been thought of
as either resembling or being related to the Chytridiales (Schneider,
1884; TrBgouboff, 1913), the Microsporidia (LBger and Duboscq, 1909 ;
LBger and Hesse, 1921), the Mycetozoa (LBger and Duboscq, 1909), and
(6
175
dextrose agar, nutrient agar, and thioglycollate agar. All his attempts
have been unsuccessful although mature spores maintained their jntegrity in these media for 3 months.
Pathology. H . tumefacientis causes tumefactions (swellings) in its
host’s tissues. These swellings vary in size and are light brown or tan
in color. Microscopically, parasites in the digestive gland tubules tend
to be subepithelial, situated towards the peripheral margin of each cell.
As they develop, they displace the epithelial cells and may inhibit
their growth. Despite these histopathological alterations, no necrosis
of mussel tissues or neoplasms occur. The fate of infected mussels is
not known.
E. Subphylum CNIDOSPORA
Class Microsporidea
The microsporidean genus Chytridiopsis includes two species known
to parasitize commercially important marine molluscs. These protozoa,
at one time considered to be sporozoans, are now considered to be
members of a distinct subphylum, the Cnidospora.
1. Chytridiopsis mytilovum (Field, 1924). (Figs. 66-76)
(Order Microsporida; family?)
Chytridiopsis mytilovum was originally superficially described by
Field (1924) who was making a comprehensive study of the host,
Mytilus edulis. Although he admitted little familiarity with the
Sporozoa,” he felt obliged to report the occurrence of this parasite in
the ova of the mussel. He stated that: “ It was finally identified for
the author through the kindness of Dr. Gary N. Calkins, of Columbia
University, as a probably new species of the genus Haplosporidium.”
As the result, Field briefly described the parasite, namedit H . rnytilovum,
and promised to investigate it further. Unfortunately, he died soon
thereafter and no additional studies were made.
Sprague rediscovered H . mytilovum in the ova of the same host,
Mytilus edulis, collected at Ocean City, Maryland. After critical study,
he (Sprague, 1963) stated that it does not belong to the genus Haplosporidium and later (Sprague, 1965a) transferred it to Chytridiopsis, a
genus the systematic position of which remains uncertain. I n his
discussion, Sprague pointed out that Chytridiopsis has been thought of
as either resembling or being related to the Chytridiales (Schneider,
1884; TrBgouboff, 1913), the Microsporidia (LBger and Duboscq, 1909 ;
LBger and Hesse, 1921), the Mycetozoa (LBger and Duboscq, 1909), and
(6