326 



Cheng, Thomas C.,and Richard W. Burton. 1965. 



The American oyster and clam as experimental intermediate hosts of 

 Angiostrongylus cantonensis . J. Parasitol. 51(2): 296. 



A. cantonensis , the metastrongylid rat lungworm, is an etiologic agent in 

 human eosinophilic meninogoencephalitis in the Pacific area. Infection of 

 the host usually is established by ingestion of molluscan intermediate hosts 

 containing 3rd-stage larvae. A. cantonensis has not been reported from 

 North America, but it was considered to be of public health importance to 

 determine if North American edible mollusks could serve as potential 

 vehicles for infection. Six days after infection, young quahogs 2.5 to 3 cm 

 long contained viable 2nd-stage nematode larvae in process of molting, and 

 3rd-stage larvae. Young white rats were infected successfully with these 

 3rd-stage larvae. It would be important to determine if animals which 

 customarily defecate in the vicinity of shellfish beds can serve as definitive 

 hosts of A . cantonensis . - J.L.M. 



327 



Cheng, Thomas C, and David A. Foley. 1975. 



Hemolymph cells of the bivalve mollusc Mercenaria mercenaria: An electron 

 microscopical study. J. Invert. Pathol. 26(3): 341-351. 



Hemolymph cells of M. mercenaria were studied with a transmission electron 

 microscope. Three morphological cell types were recognized: granulocytes, 

 hyalinocytes , and fibrocytes. Their -fine structural characteristics were 

 described. So-called fibrocytes probably are granulocytes at the terminal 

 phase of their physiologic cycle relative to degradation of phagocytized 

 foreign materials, because they included large aggregates of glycogen 

 granules in their cytoplasm and contained primary phagosomes enclosing 

 partially degraded exogenous material and digestive lamellae. Cytoplasmic 

 granules of hard clam granulocytes are delimited by a unit membrane and 

 include a homogeneously electron-dense material. Crassostrea virginica 

 cytoplasmic granules in granulocytes have a complex wall. Lipidlike 

 droplets are reported for the first time in granulocytes and hyalinocytes 

 of M. mercenaria. - modified authors' abstract - J.L.M. 



328 



Cheng, Thomas C, and Erik Rifkin. 1970. 



Cellular reactions in marine molluscs in response to helminth parasitism. 

 In A symposium on Diseases of Fishes and Shellfishes. Stanislas F. 

 Snieszko (edj . Am. Fish. Soc, Washington, D.C. Spec. Pub. 5: 443-496. 



Lipase activity, and presence of a dehydrogenase and cholinesterase have 

 been reported in leucocytes of Mercenaria mercenaria. When cercariae of 

 the trematode Himasthla quissetensis were introduced experimentally into 

 M. mercenaria , each metacercaria secreted a non-cellular inner cyst wall 

 around itself, stimulated by some component in hemolymph of the clam. An 

 outer cyst wall of host leucocytes and either myofibers or connective 

 tissue fibers, also was formed. When cercariae were induced to encyst 

 in vitro in whole blood of M. mercenaria , leucocytes were attracted to 

 form an envelope around the inner wall, but when cercariae did not encyst 

 this reaction did not occur. Chemotaxis must be the mechanism that 

 attracts leucocytes to the parasite-secreted wall, but the chemical nature 

 of the attractant is not known. These observations on hard clam were cited 

 from other papers abstracted elsewhere in this bibliography. The paper also 

 contains a section on pearl formation or "nacrezation" , which is of general 

 interest to students of mollusks, although hard clam is not mentioned 

 specifically. - J.L.M. 



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