32 American Seashells 



tide. The Coquina Clam, Donax, is faced with much the same problem of 

 making the most of high tides but, in contrast to the sedentary hfe of its 

 oyster cousin, it leads a very active existence on the sandy beaches along the 

 open ocean. It is an attractive sight when a scouring wave suddenly studs 

 the white beach with dozens of brightly hued clams. The tumbling motion 

 and sudden exposure to light act as a stimulus to the clam which instantly 

 thrusts out its small muscular foot and rapidly pulls itself down into the 

 sand again. During the three or four hours in which the waves are sweeping 

 the middle and upper sections of the beach, the tiny clams may be uncovered 

 and obliged to burrow down again several hundred times. 



While many clams prefer clean sand as a habitat, others are habitual 

 mud-dwellers. The handsome Angel Wing, Barnea costata, is usually found 

 in mud so soft and deep that Florida collectors find it extremely difficult to 

 reach them. The Angel Wing is usually located one or two feet below the 

 mud surface and maintains its connection with the bay's waters with its long 

 siphon. Because of its popularity as a souvenir and collector's item, methods 

 have been devised to collect them at high tide from a boat or barge. Power- 

 ful jets of water are forced through hoses, the mud is swept away from the 

 clams, and then hand-nets are employed to gather them. In more shallow 

 regions where a mixture of sand in the bay bottom permits walking, the 

 exposed Angel Wings are gathered by hand at the next low tide. 



The majority of marine clams live in a substrate of sandy mud, but a 

 few have become specialized to the extent of making burrows in exceedingly 

 compact clay, as in the case of the Arctic Saxicave, Hiatella arctica, and 

 the False Angel Wing, Petricola. A few groups such as the Date Mussels, 

 Lithophaga, and the Piddocks, Pholas, burrow into corals, other shells or 

 soft rocks such as sandstone and limestone. The shipworms, Teredo and 

 Bankia, are expert at drilling out their long, tube-like homes in wooden 

 planks of ships, wharf pilings, and manila hemp. So too is the Wood Piddock 

 or Martesia. 



A large proportion of bivalves are found in shallow water, but many 

 others are typically deep-water dwellers. The bathymetric range for some 

 species may be narrowly defined in the case of certain scallops. Dipper 

 Clams {Cuspidaria) and astartes. On the other hand, some species found in 

 a few feet of water may also occur in depths of over two miles. One species 

 of Abra Clam, Abra projundorum E. A. Smith, has been dredged in the 

 mid-North Pacific at a depth of 2,900 fathoms — over three miles! 



HOW THEY GROW 



The shelly valves of clams are the product of the fleshy mantle. This 

 thin, leaf-like organ covers the animal as the flyleaves cover the body of a 



