1819 



Tripp, M. R. 1963. 



Cellular responses of mollusks. Ann. N.Y. Acad. Sci. 113(1): 467-474. 



Most information on lamellibranch tissue responses has been obtained from 

 histopathological studies of diseased oysters. The paper cites no specific 

 information on Mereenaria mereenaria but the general principles would apply. 

 Responses of mollusks to foreign materials fall into 3 categories: 1) no 

 appreciable cellular response; 2) small particles in tissues and blood sinuses 

 may be phagocytized and either carried through epithelia to the exterior or 

 degraded intracellularly; and 3) foreign material in lesions may be infiltrated 

 and surrounded by masses of amoebocytes, and the entire lesion is eventually 

 walled off by an epithelial layer. These leave unanswered many questions 

 about molluscan immunity. Stauber (1961) , cited elsewhere in this 

 bibliography, stated the problem clearly. Techniques of tissue culture, 

 immunology, and axenic culture will be useful experimental tools. - J.L.M. 



1820 



Tripp, M. R. 1970. 



Defense mechanisms of mollusks. J. Reticuloendothelial Soc. 7(2): 173-182. 



This review paper discusses nonspecific humoral factors, cellular responses, 

 encapsulation and antibody-like substances. The only specific reference to 

 Mercenaria mereenaria is by citation of Schmeer (1966) , abstracted elsewhere 

 in this bibliography, on antitumor activity of mercenene, an aqueous extract 

 of hard clam, and probably a glycopeptide. The author comments that the mode 

 of action of paolins and mercenene has not been demonstrated, nor has it been 

 shown that they are functional under natural conditions. A potential parasite 

 that penetrates the outer epithelium of a vertebrate may be challenged by 3 

 types of defense: 1) naturally occurring nonspecific humoral factors; 2) 

 phagocytes, fixed and motile, or other motile cells; and 3) specific antibody. 

 In mollusks nonspecific humoral factors may act directly to destroy foreign 

 material, or they may enhance phagocytosis. Particles usually are digested by 

 phagocytes, but in some cases they survive and may even multiply. In these 

 cases cells migrate to the exterior and contained particles are lost by 

 attrition. Pinocytosed foreign material is carried across epithelia also; 

 there is no evidence that it is digested intracellularly. Large particles 

 are walled off by capsules of leucocytes and connective tissue. Antibodies 

 are not known to be produced in mollusks , but there is some evidence that 

 specific effective humoral factors may be induced by infection with, or 

 injection of, appropriate foreign substances. - J.L.M. 



1821 



Trueman, E. R. 1966. 



Bivalve mollusks: Fluid dynamics of burrowing. Science 152(3721): 523-525. 



Bivalves that live in sand or mud, like Mereenaria, all use essentially 

 similar steplike digging movements. Each step includes a cycle of activities 

 including the following successive actions: 1) extension of foot; 2) closure 

 of siphons; 3) adduction of the valves; 4) pedal dilation; 5) contraction of 

 pedal retractor muscles, causing movement of shell into the sand; 6) followed 

 by a short period of relaxation when the valves open. Between successive 

 cycles is a static period of variable duration when the foot is extended, 

 probing more deeply into the substrate, and the shell remains stationary or 

 is slightly raised. Pedal retraction usually occurs in two phases, so that 

 posterior retraction follows anterior, and a rocking motion is imparted to 

 the shell, making for easier penetration. Protraction and probing of the 

 foot is done by intrinsic pedal muscles. Contraction of transverse and 

 protractor muscles causes extension of retractors, generating only low 

 pressures in the pedal hemocoel. In the digging cycle, adduction of the 

 shell causes a major increase of pressure in pedal hemocoel; pressure is 

 sustained by retraction of foot, which occurs immediately after adduction. 

 At adduction, hydrostatic pressure is increased not only in the foot but 

 throughout the body. The effect of adduction is to put the hinge ligament 

 under a strain that causes valves to reopen. Internal pressure ejects water 

 from the mantle cavity and blood into the pedal hemocoel. Ejection of water 

 liquifies sand adjacent to the shell immediately before retraction, allowing 



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