to mantle was usually fatal. Intertidal species, or species from mud flats, 

 usually had greatest amounts of muscle catalase; species from sandy substrate 

 and not exposed to air the least. Difference in muscle catalase in the 2 

 species of Venus from N.C. waters was considered striking. Some clams were 

 difficult to identify, and may have been hybrids. One individual of the 

 southern quahog gave a reading of 41 for catalase, although it was less than 

 14 in all others. V. mereenaria, the northern species, can live on sandy 

 beaches, mud flats, even in marsh grass areas, can tolerate semi-stagnant 

 conditions, and can live on beaches exposed at low tide 2/3 rds of the time. 

 V. eampeehiensis lives in sand or on mud shoals along river channels, at low 

 water line or at considerable depths. It seldom occurs more than a few inches 

 above low water level. These differences in tolerance and vertical 

 distribution help to explain differences in catalase and 0/c quotient. In 

 V. mereenaria the lower 0/c quotient is associated with the greater power of 

 survival of mature clams as compared with young when kept out of water. 

 Relatively inactive species like V. mereenaria have more muscle catalase than 

 active forms. The function of catalase is to decompose H2O2 formed in tissues 

 preventing its accumulation in toxic amounts. Molecular (inactive) 02 appears 

 in the reaction, thus it does not promote oxidation directly, but is still 

 available for oxidases to act upon. A large amount of catalase, by destroying 

 H2O2 , retards oxidation with peroxidase, but does not entirely prevent it, 

 since peroxidase reacts with a much lower concentration of peroxide than does 

 catalase. Thus, the role of catalase in animals exposed to oxygen deficiency 

 is to conserve metabolic activity. - J.L.M. 



869 



Hopkins, Hoyt S. 1939. 



Seasonal differences in the oxygen exchange and glycolysis of tissues in the 

 clam Venus mereenaria. Anat. Rec. 75 (suppl.) : 133. 



An age difference in O2 respiration had the same magnitude winter and summer. 

 In summer, respiratory rate of gill tissue was 21% greater in young clams than 

 in old when respirometers were oscillated, 16.8% greater when not shaken. In 

 winter and early spring 02 exchange in gills of young clams was 7.4% higher 

 than in old with a shaking rate of 3 oscillations/min, 6% lower without 

 shaking. At a shaking rate of 60, 02 exchange was 13.3% higher. Mantle 

 tissue from young clams had respiration rates in winter more than 20% greater 

 than from old clams, thus resembling muscle. In winter, muscle tissue of old 

 clams was 164 ul CO2 liberated from seawater+bicarbonate in N, in summer 174; 

 young clams in winter 161, summer 193. In winter gill of old clams 117, 

 summer 160; gill of young in winter 68, summer 193. Mantle tissue, like 

 muscle, showed small seasonal differences: old clams in winter 348, summer 337, 

 young in winter 302, summer 373. Results showed a selective condition of 

 hibernation in gill metabolism, particularly of young clams, related to their 

 sluggish activity in winter and spring. - J.L.M. 



870 



Hopkins, Hoyt S. 1941. 



Growth rings as an index of age in Venus mereenaria. Anat. Rec. 81 (suppl.) : 

 53-54. 



In Beaufort, N.C. clams marked by notching the shell margin were recovered 

 after 1 to 7 yrs. With few exceptions, newly formed growth layers in shell 

 sections corresponded with number of years of growth. Exceptions were large, 

 old clams with slow growth rate; small clams planted near high tide mark, 

 where growth was retarded; occasional clams recovered from shelly bottoms, 

 which showed evidence of interrupted .growth. In slow-growing clams shell 

 laminae were so thin as to be difficult to see, and winter growth so 

 indistinct as to be overlooked. Age of old or retarded clams therefore 

 could be underestimated. Clams from N.C, in sections of shells, showed as 

 many as 45 growth layers. In some from N.Y. as many as 7 to 8 layers were 

 seen, and these clams were larger. (Abstracter's note: it is not clear if 

 layers means years.) - J.L.M. 



243 



