924 



Jeffries, H. Perry. 1972. 



A stress syndrome in the hard clam, Meroenaria meroenaria. J. Invert. 

 Pathol. 20(3) : 242-251. 



Hard clam, Mercenavia meroenaria, shows a general response to environmental 

 variation and infection. The molar ratio of free taurine to glycine in 

 gill and mantle tissues climbs above 3, while alpha-amino acids and 

 carbohydrates decrease. Subtle adjustments in the total pattern of free 

 amino acids and fatty acids also occur, but these can be readily seen by 

 changes in biochemical diversity and equitability . In an estuary long 

 polluted with hydrocarbons, the clam population had a patchy distribution 

 and a short life-span. These variations were attributed to a culmination 

 of abnormal complications superimposed on natural responses to a seasonally 

 changing environment. The process apparently starts after a tarlike 

 irritant collects in epithelial tissue and eventually plugs the renal sac. 

 This leads, indirectly, to invasion of shells by Polydora sp. , a polychaete 

 rarely found in hard clams . A syndrome with many facets soon becomes 

 clear, but the situation can be identified and its results predicted by 

 observing responses of taurine and glycine in stressed and normal 

 populations. When the molar ratio of taurine to glycine is less than 3, 

 the population is normal; if it lies between 3 and 5, a chronic stress is 

 indicated; at values greater than 5 the situation is acute. - modified 

 author's abstract - D.L. 



925 



Jegla, Thomas C . , and Michael J. Gree.nberg. 1968. 



Structure of the bivalve rectum. I. Morphology. Veliger 10(3): 253-263. 



Meroenaria meroenavia 75 to 125 mm long had rectums with an average diameter 

 of 1400 u, height of columnar cells and basement membrane 81.4 u, thickness 

 of the wall 284.5 u, and ratio epithelium to wall 0.29; Meroenaria eampech- 

 iensis 75 to 150 mm long had rectums with an average diameter of 1270 u, 

 height of columnar cells and basement membrane 40.7 u, thickness of the wall 

 181.5 u, and ratio epithelium to wall 0.22. Total range of these average 

 measurements in 38 bivalves was diameter of the rectum 5140-64 u, height of 

 columnar cells and basement membrane 116.0-8.5 u, thickness of the wall 

 406.3-8.5 u, and ratio epithelium to wall 1.0-0.05. Variation was large, 

 but familial similarities in rectal construction were found. - J.L.M. 



926 



Jegla, Thomas C.,and Michael J. Greenberg. 1968. 



Structure of the bivalve rectum. II. Notes on cell types and innervation. 

 Veliger 10(4): 314-319. 



Probably no peristalsis occurs in the intestine of Meroenaria meroenaria, 

 but spontaneous contractions of in vitro preparations of rectums have been 

 observed. The histological architecture of the rectum supports the view 

 that conduction in this organ is by way of nerves rather than muscle. Ob- 

 servations of Meroenaria rectum show that although longitudinal nerve fibers 

 are present, they are small. There are ganglion cells present. Multiple 

 innervation of muscle cells is not ruled out. The muscle fibers appear to 

 to be smooth muscle having the classical appearance at physiological lengths 

 and oblique or helical bands at excessively short lengths. In relaxed or 

 stretched rectums the muscle fibers are without visible fibrils or have 

 fibrils parallelling the long axis of the fiber, whereas in highly con- 

 tracted rectums dense bands appear in the fibers which give the appearance 

 of a diamond lattice pattern. The myo-fibrils do not appear to be helically 

 wound around the periphery as they are in the heart, but are dispersed 

 throughout the core of the fiber. - J.L.M. 



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