4. ANALYSIS O F FACTORS INVOLVED IN SYMBIOSIS
103
Whether a pathogenic effect on the oyster resuIts from infection is not
known, with no histopathological indications noted other than the extensive
cyst formation, but the Condition Indices of oysters from numerous locations
in Pearl Harbor (Hawaii) were consistently much lower than normal for the
species for the season of the year.
After commenting on the availability of nutrients and the crowded
growing conditions, Sparks has concluded that it remains unknown
whether the lower Condition Index (a measure of fatness) is caused
by the parasite or crowding. I n a subsequent study of the same
larval cestode, Cheng (1966a) has demonstrated that the cyst is of host
origin and that delayed encapsulation, resulting in the death and resorption of the parasite, occurs. The fibrous encapsulation of another
larval cestode, Echeneibothrium sp., in Venerupis staminea has been
reported by Sparks and Chew (1966). These authors have suggested
that the encapsulating fibers are collagenous, but since they have only
examined sections stained with hematoxylin and eosin one cannot be
certain of the chemical nature of the fibers. Recently Rifkin and Cheng
(1967), using histochemistry, have demonstrated that these fibers are
reticular rather than collagenous.
Digenetic trematodes comprise the largest group of known parasites
of marine molluscs (see Fretter and Graham, 1962). Damage to the
tissues of molluscs caused by trematode larvae range from slight,
involving only the dislocation of the surrounding hepatopancreatic
tubules (Pratt and Lindquist, 1943), to rather severe changes, involving
mechanical destruction of cells coupled with autolysis and parasiteinduced lysis (Faust, 1917, 1920; Faust and Meleney, 1924; Hurst,
1927 ; I?. G. Rees, 1934 ; W. J. Rees, 1936a; Fatham and Porter, 1936 ;
Agersborg, 1924; La1 and Premvati, 1955; Cheng and James, 1960;
Cheng and Snyder, 1962a; Cheng and Burton, 1965b). The types of
histo- and cytopathological changes have been reviewed by Cheng and
Snyder (1962a).* Such alterations are tabulated below.
1. Fatty bodies accumulate in hepatopancreatic cells.
2 . Vacuoles appear in the cytoplasm of hepatopancreatic cells.
3. Karyolysis occurs.
4. Sloughing of tissues occurs.
5. Formation of fibromata and granulomata occurs.
6. The tunica propria surrounding the hepatopancreas may be ruptured
7. Granular substances are secreted by host cells.
8. Release of cell pigments occurs.
and penetrated by foreign bodies.
* For another general review of pathologic changes in gastropods due to helminths,
see Wright (1966).
103
Whether a pathogenic effect on the oyster resuIts from infection is not
known, with no histopathological indications noted other than the extensive
cyst formation, but the Condition Indices of oysters from numerous locations
in Pearl Harbor (Hawaii) were consistently much lower than normal for the
species for the season of the year.
After commenting on the availability of nutrients and the crowded
growing conditions, Sparks has concluded that it remains unknown
whether the lower Condition Index (a measure of fatness) is caused
by the parasite or crowding. I n a subsequent study of the same
larval cestode, Cheng (1966a) has demonstrated that the cyst is of host
origin and that delayed encapsulation, resulting in the death and resorption of the parasite, occurs. The fibrous encapsulation of another
larval cestode, Echeneibothrium sp., in Venerupis staminea has been
reported by Sparks and Chew (1966). These authors have suggested
that the encapsulating fibers are collagenous, but since they have only
examined sections stained with hematoxylin and eosin one cannot be
certain of the chemical nature of the fibers. Recently Rifkin and Cheng
(1967), using histochemistry, have demonstrated that these fibers are
reticular rather than collagenous.
Digenetic trematodes comprise the largest group of known parasites
of marine molluscs (see Fretter and Graham, 1962). Damage to the
tissues of molluscs caused by trematode larvae range from slight,
involving only the dislocation of the surrounding hepatopancreatic
tubules (Pratt and Lindquist, 1943), to rather severe changes, involving
mechanical destruction of cells coupled with autolysis and parasiteinduced lysis (Faust, 1917, 1920; Faust and Meleney, 1924; Hurst,
1927 ; I?. G. Rees, 1934 ; W. J. Rees, 1936a; Fatham and Porter, 1936 ;
Agersborg, 1924; La1 and Premvati, 1955; Cheng and James, 1960;
Cheng and Snyder, 1962a; Cheng and Burton, 1965b). The types of
histo- and cytopathological changes have been reviewed by Cheng and
Snyder (1962a).* Such alterations are tabulated below.
1. Fatty bodies accumulate in hepatopancreatic cells.
2 . Vacuoles appear in the cytoplasm of hepatopancreatic cells.
3. Karyolysis occurs.
4. Sloughing of tissues occurs.
5. Formation of fibromata and granulomata occurs.
6. The tunica propria surrounding the hepatopancreas may be ruptured
7. Granular substances are secreted by host cells.
8. Release of cell pigments occurs.
and penetrated by foreign bodies.
* For another general review of pathologic changes in gastropods due to helminths,
see Wright (1966).