The tree snail LigMus fasciatus roseatus is but one of 

 many with strikingly colored shells in southernmost 

 Florida. During the rainy season it feeds on fungi, 

 but in dry seasons withdraws into the shell and at- 

 taches itself firmly to a tree. { Ralph Buchsbaum ) 



rock it cements its left valve, and begins to thicken 

 both halves of the shell until they become quite ir- 

 regular. There it reaches a diameter of more than 4 

 inches, still ready to snap its right valve closed and 

 to squirt water at any animal that disturbs it. 



Oysters (Ostraea) settle after an even briefer 

 swimming experience. At an age of about two weeks 

 the ciliated larva sinks to the bottom, forms a minute 

 shell, and attaches itself to some solid object. This 



stage is known as a "spat." Unless it finds a suitable 

 support it dies. But once "set," it proceeds to de- 

 velop into a reasonable facsimile of its parent. 



European and Pacific oysters begin their develop- 

 ment while the fertilized eggs are retained in the gills 

 of the female, whereas the Atlantic oysters of Amer- 

 ica shed both eggs and sperm, letting fertilization 

 occur in the sea. Since a Maryland oyster may release 

 sixteen million eggs at a time, and repeat the per- 

 formance several times a year, oysters seem unlikely 

 to die out unless the spats fail to find suitable sup- 

 ports upon which to set. 



Oyster culture is largely a matter of providing an 

 attractive bottom and preventing overcrowding so 

 that each oyster will grow well formed and to a mar- 

 ketable size. Oystermen also try to reduce the num- 

 ber of sea stars preying upon growing oysters, and to 

 find ways to discourage Urosalpiux and other carniv- 

 orous snails that thrive in oyster beds at the expense 

 of the industry. Pearl oysters (Meleagrina) of warm 

 seas and Japanese waters are cultured too because 

 they appear to produce better pearls; the quality of 

 their meat is low. 



Pelecypods include quite a number of other fixed 

 clams. Of these the hoof shells (Chama) of tropical 

 waters and the eastern Pacific take the other alterna- 

 tive, aflixing themselves by their right valves. Jingle 

 shells (Anomia) hold the left valve down but in a 

 very strange way. The valve next to the rock has a 

 hole in it, and the closing muscle of the mollusk goes 

 through the hole to an attachment area on the sup- 

 port. Both valves of a jingle shell are extremely thin, 

 and they may be ridged or smooth and highly pol- 

 ished. If several left valves of Anomia are strung on 

 a cord and shaken gently, they give the jingling 

 sound for which the shells are named. 



BURROWING CLAMS 



Other pelecypods burrow into sandy and muddy 

 bottoms, remaining out of sight for most or all of their 

 lives. Among the most active of them are the bean 

 shells or coquinas (Donax), which live in the sur- 

 face sands between tide marks and just below low- 

 tide level along many of the world's coasts. 



A bird or a beachcomber can watch these Vi- to 

 1-inch shellfish simply by standing quietly as waves 

 expend their energy on a gradually sloping beach. 

 As the water hurries in, it carries sand with it and ap- 

 parently buries the Donax clams more deeply than 

 they tolerate. By dozens or hundreds or thousands, 

 they shove themselves up into the water just about 

 the time the wave reaches its highest point. For a 

 moment they may lie on their sides on the sand in 

 the clearing, momentarily motionless water, feeding 

 in the liquid that covers them to a depth of a few 

 inches. Then the water rushes out again, rolling over 

 and over those little clams that have not dug them- 



188] 



