NOTE Smghas et al.: Occurrence of Echeneibothnum in the calico scallop 



181 



migrated to eastern coastal waters. It is possible that 

 parasitized intermediate and/or final host species ei- 

 ther were introduced or migrated into the area. 



Invasion of molluscan gonadal tissue by parasitic 

 flatworms has been described as a secondary invasion, 

 with the hepatopancreas (digestive gland) serving as 

 the primary site. The resulting damage to the gonad, 

 including atrophy and eventually destruction of the 

 germinal epithelium, is believed to be a combination 

 of mechanical pressure and nutrient deprivation (Cheng 

 1967). However, within the gonads of parasitized 

 Argopecten gibbus, these changes were not apparent. 

 Developing and mature eggs in the acini were identi- 

 cal in morphology to the eggs seen in non-parasitized 

 tissue, and did not differ significantly in diameter 

 (Singhas 1992). The only obvious difference was the 

 higher numbers of hemocytes surrounding the germi- 

 nal epithelium in infected scallops. The most exten- 

 sive tissue damage in parasitized A. gibbus occurred 

 in the epithelium of the intestinal loop. This damage 

 consisted of alterations in intestinal epithelial cell 

 shape and structural integrity, similar to those de- 

 scribed by Cheng (1967) for hepatopancreatic tissue. 



Failure of the local commercial crop of A. gibbus 

 coincided with the appearance of Echeneibothrium in 

 1991 (P. Phalen, N.C. Div. Mar. Fish., Morehead City 

 NC 28557-0769, pers. commun.). It is uncertain if the 

 Echeneibothrium infestation contributed directly to this 

 failure, because this species is known to undergo dra- 

 matic fluctuations in number (Moyer & Blake 1986). 

 However, the commercial failure of A. gibbus in Florida 

 during January-February 1991 was attributed to a 

 Protoctistan parasite, Marteilia sp. (Blake & Moyer, 

 1992). Parasitism may therefore be an important fac- 

 tor in the population biology of A. gibbus, and merits 

 further investigation. 



Acknowledgments 



We would like to gratefully acknowledge Dr. Thomas 

 Cheng for his identification of the organism described 



in this Note, and for his editorial assistance with the 

 manuscript. Thanks also to Dr. Charles Singhas for 

 technical and editorial assistance, and to Dave Taylor 

 of the N.C. Division of Marine Fisheries for his assis- 

 tance in collections. 



Citations 



Cake, E.W. 



1977 Larval cestode parasites of edible mollusks of the 

 NE Gulf of Mexico. In Shumway, S.E. (ed.), Scal- 

 lops: Biology, ecology, and aquaculture, p. 482- 

 483. Elsevier Sci. Publ., Amsterdam. 

 Blake, N.J., & Mj\. Moyer 



1992 Mass mortality of calico scallops, Argopecten 

 gibbus, resulting from an Ascetosporan infection 

 [abstract]. In 25th Annu. Meet., Soc. Invertebr. 

 Pathol., 16-21 Aug. 1992, Heidelberg, Germany. 

 Cheng, T.C. 



1967 Marine molluscs as hosts for symbiosis. Adv. 

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 Cummins, R. Jr., A.L. Rhodes, J. Easley, B. Anderson, 

 J.C. Cato, F. Prochaska, P. Fricke, F. Munden, & B. 

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1981 Profile of the calico scallop fishery in the South 

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 Humason, G.L. 



1962 Animal tissue techniques. W.H. Freeman, San 

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 Moyer, MA., & N.J. Blake 



1986 Fluctuations in calico scallop production (Argo- 

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 Singhas, L.S. 



1992 Reproductive periodicity and gonadal develop- 

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 Sparks, A.K., & K.K. Chew 



1966 Gross infestation of the littleneck clam, Venerupis 

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