2094 



Cheng, Thomas C. 196 7. 



Marine Molluscs as Hosts for Symbioses. With a review of known parasites of 

 commercially important species. In Advances in Marine Biology, Vol. 5, 

 Sir Frederick S. Russell (ed.) . Academic Press, London and New York, xiii + 

 424 p. 



Vogel (1933) reported that a German became infected with the intestinal 

 trematode Himasthla muehlensi after eating several raw "littlenecks" 

 (Mereenaria mereenaria) on the half-shell in New York. Recently Cheng and 

 Burton (1965) demonstrated that the nematode Angiostrongylus cantonensis 

 can develop to the infective third-stage larva in M. mereenaria, which, 

 since it is commonly eaten raw, could serve as a potential transmitter. The 

 plasma of several species of pelecypod, including the hard clam, will induce 

 encystment of cercaria of Himasthla quissetensis. It is believed that in 

 nature, once the cercariae succeed in penetrating one of these mollusks, 

 contact with plasma in the open circulatory system induces encystment and 

 the cercaria develops into a metacercaria. The decarboxylation product 

 taurine has been identified in almost all marine mollusks examined, including 

 M. mereenaria' (Allen 1961). Himasthla quissetensis of the Class Trematoda 

 has been found in M. mereenaria. Himasthla muehlensi was described from a 

 human who had eaten raw hard clams in New York, and later, on returning to 

 Germany, complained of gastrointestinal disturbances. It had not been found 

 yet in M. mereenaria in America. It is uncertain whether it is distinct 

 from H. quissetensis . Tissues of M. mereenaria surrounding H. quissetensis 

 cysts undergo chemical change. Among these changes is accumulation of short- 

 chained fatty acids, provisionally identified as butyric acid among others. 

 It was postulated that if sufficient numbers of clams which include toxic 

 short-chained fatty acids in their tissues are ingested, gastrointestinal 

 disturbances could occur. Angiostrongylus eantonensis is a nematode, a 

 metastrongylid lungworm of rats. It is not a natural parasite of salt-water 

 clams, but Cheng and Burton (1965) showed that young quahogs can be infected 

 experimentally. The snail Odostomia impressa will not feed on Mereenaria, 

 a few may crawl on the clam but do not stay. Odostomia bistularis will be- 

 come attached to M. mereenaria but is not likely to be an important parasite. 

 Odostomia seminuda also will become attached to M. mereenaria according to 

 Boss and Merrill (1965). Mytieola porreeta of the Class Crustacea has been 

 found in M. mereenaria in the intestine (Humes 1954) . Myocheres major was 

 found in mantle cavity of M. mereenaria by Williams (1907) and Pearse (1947) . 

 Ostrineola gracilis was found by Humes (1953) in mantle cavity of hard clam 

 from Barataria Bay, La. Neopanope texana, a crab, preys upon young M. 

 mereenaria according to Landers (1954) . - J.L.M. 



2095 



Cheng, T. C. 1976 



The role of lysosomal enzymes in molluscan immunity. Cdn. Fed. Biol. Soc. , 

 19th Ann. Meeting: 158 (abstract 630) . 



Cytoplasmic granules of hard clam, Mereenaria mereenaria, are lysosomes. A 

 number of lysosomal enzymes from several species of mollusk have been iden- 

 tified and characterized. These include lysozyme, acid and alkaline phos- 

 phatases, 6-glucuronidase, lipase, and aminopeptidase. When whole hemolymph 

 is challenged with bacteria in vitro and in vivo, the levels of activity of 

 all the lysosomal enzymes studied are elevated within phagocytes; however, 

 only certain ones are released from cells into serum. It is concluded that 

 those which are released can act upon susceptible bacteria extracellulary . 

 - modified author's abstract - J.L.M. 



2096 



Cheng, Thomas C. 19 76. 



Humoral immunity in molluscs. In Proc. First International Colloquium on 

 Invert. Pathol, and IXth Ann. Meeting, Soc. Invert. Pathol. Printing Dept. , 

 Queens Univ.: 190-194. 



In Mereenaria mereenaria the cytoplasmic granules of granulocytes are not 

 secondary phagosomes but true lysosomes. These deposit their enzymes into 



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