CHAPTER IV 

 GENERAL ANATOMY 



Page 



IntrodiK'tory remarks - 65 



Methods of study., 65 



Organs underlying the shell 66 



Organs underlying the mantle '0 



The visceral mass 71 



Nervous system "l 



Anatomiea! peeuliarities "2 



Bibliography "2 



Before proceeding with the detailed description 

 of the structure and function of various organs 

 in tlie oyster, it appears desirable to present a 

 general anatomical picture of this niollusk and to 

 show the arrangement and topography of the 

 various systems of organs. 



The anatomy of edible oysters is described in 

 several papers. Brooks (1905), Moore (1S9S), 

 Churchill (1920), and Galtsofi' (195S) give general 

 accounts of the anatomy of C. virginica. The 

 structure of the European oyster, 0. edulis, is 

 described by Orton (1937), Ranson (1943), and 

 Yonge (1960); a brief and partial description of 

 the anatomy of C. angitlata by Leenhardt (1926) 

 includes the histology of the species. The struc- 

 ture of the Bombay oyster, 0. cncullafa, is described 

 by Awati and Rai (1931); and a short anatomical 

 sketch of the Australian oyster, 0. comrnercialis, 

 is given by Roughley (1925). 



The anatomical sketch of an adult C. virginica 

 given in this chapter describes the principal 

 organs of the oyster as they can be seen by dis- 

 secting the mollusk and e.xaniining the preparation 

 under a low-power microscope. Details that 

 can be observed by sectioning, staining, and 

 reconstruction are described in the chapters of 

 this book dealing with the respective organ 

 systems. 



METHODS OF STUDY 



Successful dissection of the oyster depends to a 

 considerable degree on the condition and sliape of 

 the specimen selected for study. It is convenient 

 to work with broad and large oysters measuring 

 about 4 to 5 inches in lieight and containing 



FISHERY bulletin: VOLUME 64, CHAPTER IV 



lean meats. In fat or in se.xually mature speci- 

 mens the large quantities of glycogen and of se.x 

 cells covering the organs make their anatomy 

 difficult to trace. Oysters most suitable for 

 anatomical study are those which have completed 

 spawning but have not yet accumulated much 

 glycogen. In New England waters such oysters 

 can be found in September and early October. 



For dissection the oyster should be opened by 

 removing its flat (right) valve, a process facilitated 

 by fli-st narcotizing the oyster. Narcosis elimi- 

 nates the necessity of forcibly prying apart the 

 valves, a manipulation which in the hands of 

 an inexperienced person frequently results in 

 injury of the underlying tissues or, even more 

 often, to the hand of the operator by the sharp 

 edge of the shell. Another advantage of working 

 with a fully narcotized specimen is that the organs 

 and tissues remain fully expanded in their normal 

 position and are undistorted by contraction. 



The best method of narcotizing is to use technical 

 magnesium sulfate (Epsom salt) as follows: The 

 oyster is thoroughly washed and scrubbed to 

 remove fouling organisms and then placed in a 

 suitable container, about S to 9 inches in diameter 

 and 3 inches deep, filled with sea water. During 

 the first 24 hours small quantities of Epsom salt 

 are gradually added until a concentration between 

 5 to 10 percent is reached, then the oyster is left 

 undisturbed for another 24 or even 48 hours at 

 room temperature. The magnesium sulfate should 

 be added very gradually because an excess of it 

 at the beginning of narcosis may cause the oyster 

 to close its valves and thus prolong the process. 

 Additional amounts of salt may be added because 

 oysters tolerate much higher concentrations of 

 magnesium sulfate and recover from it upon 

 being placed in running sea water. Completely 

 narcotized oysters do not respond to touch or 

 prick at the edge of the mantle. 



With the narcotized oyster grasped in the liand, 

 right valve uppermost, a knife is inserted between 



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