CHAPTER V 

 THE MANTLE 



Page 



Appearance 74 



Anatomy _,_ 74 



Rudimentary muscle of the mantle 79 



Histology 79 



Connective tissue 79 



Muscles 83 



Blood vessels 84 



Epithelium, tentacles, and nerves 84 



Periostracal groove and gland 86 



Suhligamental ridge 89 



Functions of the mantle 90 



Formation and calcification of shell 91 



Theories of calcification 94 



Cytological identification of calcium 101 



Sources of calcium _._ 103 



Mineralogy of calcium carbonate in molluscan shells _ 103 



Rate of calcification. - 104 



Bibliography 107 



The inner organs of all mollusks are covered 

 with a soft and fleshy fold of tissue called the man- 

 tle or pallium (Latin for cloak or coverlet). The 

 structure of the mantle is relatively simple: the 

 organ consists of a sheet of connective tissue con- 

 taining muscles, blood vessels, and nerves and is 

 covered on both sides by unicellular epithelium. 

 Many blood cells invade and wander throughout 

 the entire thickness of the mantle, infiltrating the 

 spaces (sinuses) in the connective tissue, and 

 crawling through the epithelium to aggregate on 

 the outer surface of the mantle. 



Although tlie principal role of the mantle is the 

 formation of the shell and the secretion of the 

 ligament, the organ plays a major part in several 

 other functions. It receives sensory stimuli and 

 conveys them to the nervous system and assists 

 in the shedding and dispersal of eggs during 

 spawning (see ch. XIV). The mantle also par- 

 ticipates in respiration by providing direct ex- 

 change of gases between the surface tissues of the 

 oyster and the surrounding water. It stores re- 

 serve materials (glycogen and lipids), secretes large 

 quantities of mucus and, finally, aids in excretion 

 by discarding blood cells loaded with waste 

 products. 



APPEARANCE 



The appearance of the mantle reflects the condi- 

 tion of the 03-ster. At the time of sexual maturity 



74 



it is a creamy-yellowish color. In oysters which 

 have accumulated large amounts of glycogen with 

 the onset of the cold season the mantle is white 

 and thick. In oysters of poor quality or in those 

 which have not yet recovered after spawning, the 

 mantle is so transparent that the brown or green- 

 ish color of the underlying digestive organ is 

 clearly visible through the thin and watery tissue. 

 Oysters in this condition are particularly suitable 

 for the study of muscles, blood vessels, and nerves 

 which in good quality, "fat" oysters are covered 

 by a thick layer of reserve materials. 



Pigment cells are concentrated along the free 

 edge of the mantle and in the tentacles in a band 

 varying in color from light brown to jet black. 

 Also, accunuilation of copper in the blood cells 

 may produce a distinct green coloration. Difi'er- 

 ent intensities of pigmentation are often found 

 in oysters of identical origin growing together, 

 and cannot be correlated with geographical loca- 

 tion or type of botton\. 



ANATOMY 



For a detailed study of the mantle the oyster 

 should be fully narcotized by Epsom salt (see 

 p. 65) or by refrigerating it overnight at a tempera- 

 ture of about 2° to 4° C. After the valves are 

 forced apart and the body dissected along the 

 median plane, the two halves of the oyster are 

 left attached to their respective valves and the 

 mantle is preserved in its natural position by hav- 

 ing a large quantity of fixing fluid poured over it. 

 Portions of the mantle required for study are cut 

 off, stained, delwdrated, cleared, and mounted. 

 In this way very satisfactory whole mounts can 

 be obtained. 



The two lobes of the mantle are joined together 

 at tlie dorsoposterior margin, and form a cap or 

 hood which covers the mouth and the labial 

 palps (fig. 71). Along the anterior and ventral 

 sides of the body the lobes are free and follow the 

 curvature of the shell. When the oyster opens 

 its shell the mantles separate with the valves to 



FISHERY bulletin: VOLUME 64, CHAPTER V 



