PORTER: REPRODUCTIVE CYCLE OF MYA ARENARIA 



sexes, while in 1972 many of the females failed to 

 spawn completely although the discharge of male 

 sex products seemed complete. 



DISCUSSION 



The gonadal inclusions of male and female 

 soft-shell clams are distinctive. Coe and Turner 

 ( 1938) state that the origin of these inclusions is 

 partly from cytoplasmic activity of follicle cells 

 and partly from cyto lysis of gametes. The fact that 

 all immature clams in the process of sexual dif- 

 ferentiation were found to be developing inclu- 

 sions characteristic of their sex seems to verify 

 cytoplasmic activity of the follicle cells as one 

 origin of these inclusions. In older male clams, the 

 method of formation of the multinucleated cells 

 first described by Coe and Turner ( 1938) as pycno- 

 tic nucleii and later by Shaw ( 1965) as sperm balls, 

 needs further study. If the unspawned sperm are 

 retained by the male clam as sperm balls as re- 

 ported by Shaw (1965) and as my observations 

 indicate (Figure Ic), then perhaps cytoplasmic ac- 

 tivity of the follicle cells is the major method by 

 which the inclusions are formed. In female clams 

 the exact relationship between cytolysis of un- 

 spawned ova and the formation of inclusions is not 

 known. The single row of follicle cells which form 

 almost immediately at the basal membrane of the 

 alveoli in spent female clams already contain a 

 number of inclusions (Figure 3d) before any of the 

 unspent ova have undergone cytolysis. The origin 

 and function of gonadal inclusions in both sexes 

 requires further investigation. 



The gametogenic cycle of the soft-shell clam at 

 Skagit Bay is identical to that reported for clams 

 from the east coast (Coe and Turner, 1938; Shaw, 

 1962, 1965; Pfitzenmeyer, 1965; Ropes and Stick- 

 ney, 1965). The single spawning cycle per year, 

 from late May to early September, is similar to 

 that described for studies in eastern Canada (Staf- 

 ford, 1912; Battle, 1932; Sullivan, 1948) and the 

 New England area (Welch, 1953 ; Ropes and 

 Stickney, 1965). 



The slight variations noted between the spawn- 

 ing cycles of 1971 and 1972 and the incomplete 

 spawning of females in 1972 cannot be explained 

 at present. 



Few hermaphroditic Mya are reported from 



^Welch, W. R. 1953. Seasonal abundance of bivalve larvae in 

 Robinhood Cove. Maine. Fourth Annual Conference on Clam 

 Research, U.S. Fish and Wildlife Service. Clam Investigations, 

 Boothbay Harbor, Maine, p. 4-6. 



other areas (Coe and Turner, 1938; Shaw, 1965). A 

 single hermaphroditic specimen was collected at 

 Skagit Bay (Figure 3f). 



ACKNOWLEDGMENTS 



I wish to extend my thanks to the Washington 

 Cooperative Fishery Unit for providing transpor- 

 tation and equipment for the study. Also, to 

 Preston E. Porter for his dutiful help with field 

 collections and to the Department of Ocean- 

 ography, University of Washington for provid- 

 ing environmental data. 



LITERATURE CITED 



Battle, H. I. 



1932. Rhythmic sexual maturity and spawning of certain 

 bivalve moUusks. Contrib. Can. Biol. Fish., New Ser. 

 7:255-276. 

 Belding, D. L. 



1930. The soft-shelled clam fishery of Massachusetts. Mass. 

 Dep. Conserv., Div. Fish Game, Mar. Fish. Serv. 1, 65 p. 



Coe, W. R., and H. J. Turner. 



1938. Development of the gonads and gametes in the soft- 

 shell clam (Mya arenaria). J. Morphol. 62:91-111. 

 Craig, E. L. 



1927. Some mollusks and other invertebrates from the 

 northwest. Univ. Colo. Stud. 16(l):63-74. 

 Deevey, C. B. 



1948. The zooplankton of Tisburry Great Pond. Bull. Bing- 

 ham Oceanogr. Collect. Yale Univ. 12(1): 1-44. 

 Edmondson, C. H. 



1920. Edible mollusca of the Oregon coast. Occas. Pap. 

 Bernice Pauahi Bishop Mus. 7(9):77-201. 

 Fitch, J. E. 



1953. Common marine bivalves of California. Calif. Dep. 

 Fish Game, Fish Bull. 90, 102 p. 



Galigher, a. E., and E. N. Kozloff. 



1971. Essentials of practical microtechnique. 2d ed. Lea 

 and Febiger, Phila., 531 p. 

 Hanks, R. W. 



1963. The sofl-shell clam. U.S. Fish Wildl. Serv., Circ. 162, 

 16 p. 

 Ivanov, a. I. 



1969. Immigration of Mya arenaria L. to the Black Sea, its 

 distribution and quantity. [In Russ., Engl, summ.] 

 Okeanologiya 9:341-347. 

 Lammens, J. J. 



1967. Growth and reproduction in a tidal flat population of 

 Macoma balthica (L.) Neth. J. Sea Res. 3:315-382. 

 Landers, W. S. 



1954. Seasonal abundance of clam larvae in Rhode Island 

 waters, 1950-1952. U.S. Fish Wildl. Serv., Spec. Sci. Rep. 

 Fish. 117, 29 p. 



Morris, P. A. 



1966. A field guide to shells of the Pacific coast and Hawaii 

 including shells of the Gulf of California. 2d 

 ed. Houghton Mifflin Co., Boston, 297 p. 



Nelson, T. C, and E. B. Perkins. 



1931. Annual report of the department of biology July 1, 



655 



