production in certain human disease processes such as arthritis and cystic 

 fibrosis. Most mantles of bivalve mollusks terminate in three folds, but 

 in M. mereenaria is an enlarged fourth fold which contains an unusually 

 large amount of mucus. Results of all histochemical procedures indicate 

 that the material in the first fold of hard clam mantle is a moderate to 

 strongly acidic, sulfated mucosaccharide. From the juxtaposition of the 

 material with shell secreting area of the mantle, it might be assumed that 

 this material plays -some role in calcification. Analysis of the structure, 

 and its similarities to those acid mucosubstances associated with calcifi- 

 cation in other organisms, may provide more information on the function of 

 glycosaminoglycans in the process of calcification. Results of histochemical 

 reactions for mucosubstances in the second fold suggest that there are prob- 

 ably two types of mucous cells present. Mucus secretions in the second fold 

 are distinctly different from those in the first fold, adding support to the 

 theory that the materials are playing far more sophisticated roles in the 

 life activity of the clam than previously suspected. If some mucopolysacch- 

 aride production in the quahog is related to osmoregulation, and if cystic 

 fibrosis is a disease associated with cellular osmoregulation, then the 

 formation and function of mucopolysaccharides in the hard clam may prove to 

 be a good lower animal model system for studying the pathology of cystic 

 fibrosis. - J.L.M. 



853 



Hillman, Robert E., and Carl N. Shuster, Jr. 1962. 



Observations on the mantle of the northern quahog, Mereenaria mereenaria L. 

 Proc. Natl. Shellf. Assn. 51: 15-22. 



The hard clam possesses a fourth fold of its mantle edge which was thought to 

 aid in voiding of debris through secretion of mucus from the mucus gland cells 

 found there. There was a cuboidal type and flask-shaped cell also present. 

 Schif f-positive material was found localized primarily in the connective 

 tissue, pallial muscle fibers, and around the groove between the sensory and 

 muscle folds. Cytochrome oxidase activity was found mainly from near the 

 hinge to the pallial line and in the distal part of the pallial border folds. 

 Succinic dehydrogenase activity was mainly in the area behind the pallial line 

 and at the inner and middle fold juncture. - D.L. 



854 



Hillman, Robert E. , and Carl N. Shuster, Jr. 1966. 



A comment on the origin of the fourth fold in the mantle of the quahog, 

 Mereenaria mereenaria. Chesapeake Sci. 7(2): 112-113. 



Based on histological similarity between the fourth fold and other sections 

 of the mantle edge of Mereenaria mereenaria and on gross observations; it is 

 determined that the fourth fold probably arises in one of three ways: (a) 

 from a split in the typical inner muscular fold, (b) as a folding-over of 

 the inner surface of the mantle margin, or (c) from a combination of the 

 inner surface of the mantle margin and the inner surface of the third mantle 

 fold. The third alternative is most probable. - J.L.M. 



855 



Hinegardner, Ralph. 1974. 



Cellular DNA content of the Mollusca. Comp. Biochem. Physiol. 47A(2): 

 447-460. 



Cellular DNA content of 110 species of Mollusca is reported, including 

 Mereenaria mereenaria and M. campeahiensis . DNA content correlates posi- 

 tively with chromosome number and, within families, with body size. The 

 more generalized molluscs tend to have higher amounts of DNa" than specialized 

 species. Mereenaria mereenaria and M. eampeehiensis each have 19 chromosomes, 

 shell length in southern quahog was 127 mm and DNA content 2.3 pg, shell 

 length in northern quahog was 102 mm and DNA content 2.0 pg. - J.L.M. 



238 



