1345 



Morris, Percy A. 1973. 



A field guide to the shells of the Atlantic and Gulf Coasts and the West 

 Indies. 3rd ed. William J. Clench (ed.) Houghton Mifflin Co., Boston, 

 xxviii+330 p. 



Range of Mevcenavia (=Venus) mevcenavia is Gulf of St. Lawrence to Fla. in 

 shallow water. Length 5 to 6 in fully grown. External morphology described. 

 Popular names include round clam, hard-shelled clam, cherrystone clam, and 

 little-necked clam. This is the chief commercial clam of east coast, second 

 to oyster in value. Many ancient shell heaps from Me. to Fla. attest to 

 extensive use by Indians. Quahog is the Indian name. Mevcenavia probably 

 comes from Indian use of colored edge of shell as wampum. Pearls are not 

 uncommon, but of no commercial value. Some recognize a subspecies notata, 

 smaller, usually lacking purple border, and with brownish, zigzag marks on 

 outer surface. A very closely related species, M. campechiensis a is larger 

 and is found from Va. to Tex. A useful glossary is included. - J.L.M. 



1346 



Morrison, Carol M., and Paul H. Odense. 1973. 



Gross structure of the adductor muscles of some pelecypods. J. Fish. Res. 

 Bd. Canada 30(10): 1583-1585. 



A study of gross structure of adductor muscles showed that pelecypods conform 

 to the following grouping: a) "Protobranchia" b) shallow-burrowing (including 

 Venus mevcenavia); c) surface-attached; and d) deep-burrowing and immobile. 

 The adductor muscle has 2 portions, translucent and opaque, except in the 

 deep-burrowing group, which have opaque muscles only. In Venus mevcenavia 

 and some other species in the shallow-burrowing group the translucent portion 

 usually is tinted pink. Translucent muscle is usually striated or obliquely 

 striated, whereas opaque muscle is usually smooth and slower. Both parts of 

 the muscle probably are used in burrowing. Fast muscle can contract briefly 

 to clear the mantle cavity of detritus. It also can close the valves rapidly 

 in adverse conditions and can keep them closed if necessary. Opaque muscle 

 contains more paramyosin than translucent muscle. The method of isolating 

 paramyosin shows that it is resistant to dehydration and to changes in pH and 

 temp. The actomyosin system of translucent muscle may be more labile and 

 susceptible to post-mortem changes than the paramyosin in opaque muscle. 

 Anterior and posterior adductors of Venus mevcenavia are fairly symmetrical. 

 The anterior is divided into translucent and opaque portions almost equal in 

 size; the posterior appears to have 3 portions, opaque, translucent, and 

 intermediate in translucency . - J.L.M. 



1347 



Morrison, George. 1971. 



Dissolved oxygen requirements for' embryonic and larval development of the 

 hardshell clam, Mevcenavia mevcenavia. J. Fish. Res. Bd. Canada 28(3): 

 379-381. 



At water temperatures of about 25°C embryological development was normal at 

 oxygen concentrations of 0.5 mg/liter and above. At 0.2 mg/liter mortality 

 was 100%.. In a single separate experiment eggs held at 0.34 mg/liter did 

 not develop beyond trochophore stage and no shells formed. Growth of larvae 

 is much better at 4.2 mg/liter and above than at 2.4 mg/liter and below. At 

 the lower level of dissolved oxygen, growth was virtually zero. Growth rate 

 returns to normal when larvae are transferred from low concentrations of 

 dissolved oxygen (short-term stress) to higher concentrations. Larval 

 growth rates were lower in flowing than in static water, probably because 

 phytoplankton cells were being lost through the overflow screen. Short-term 

 stress from low oxygen levels has no permanent effect on larval growth. 

 - J.L.M. 



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