Blake Lippi, age 10, of Pekin, Illinois for his question:
Exactly how does a clam build his shell?
The clams have been building their neat shells in the same old way for millions of years. Each baby clam inherited the pattern from his parents and he starts on this shell building program as soon as he hatches. When times are good and he has plenty to eat, he adds new ridges around the edges. As he grows older, his soft body grows bigger and he needs more room inside his shells.
The clam's two shells are hinged together with a very strong muscle. When he relaxes his hinge, the two shells part to let in the water. The hinge also can close the shells tight to shut out his enemies. The oldest part of the shell is next to the hinge. Some of the grooves in this section were made when he was a tiny baby.
Inside the shells, his boneless body is enfolded in two fleshy flaps called the mantle. This is where the sturdy shells are created, fragment by tiny fragment. Actually, each shell is a tough, hard sandwich with three layers made from chalky materials called calciums. The mantle uses a very clever plan to make the shells bigger and bigger.
The edges of the loose mantle flaps reach to the outside edges of the two shells. This part of the mantle oozes two kinds of shell building material. When these sticky materials dry, they form tough layers of shell. One forms an outer rim of the rough material that goes on top of the shells. Another forms the hard shiny inside layer of the shells. The clam adds an outer rim around his two shells during the seasons when food is plentiful and the water is pleasantly warm.
The inside layers of the shells are something special. They are made of very smooth pearly material to protect his soft body from scratches. This hard, pearly layer is added like a paint job, all over his inside walls. The special materials oozes from all over the upper surface of the mantle, which is just under the shells. When this oozy stuff dries, the inside walls of the two shells have a complete new pearly paint job.
A clam, of course, lives a very quiet life. You might think that he is out of touch with the outside world. But this is not so. When he partly opens his shells, rows of tiny threads on his body wave streams of water in and out. His gills sift and dissolve oxygen and send out waste carbon dioxide. Scraps of floating food enter his little round mouth to be digested.
From the water he also takes the calcium type chemicals he uses to build his shells. His clever mantle arranges these mini mini particles in different formations. When these oozy mixtures dry, they form the three different layers of his shells.
The clam may live in the silty sand of the sea or on the soggy floor of a stream. His private water supply is part of the world wide streams and oceans. This water dissolves all sorts of chemicals from the rocks. When it enters the clam, he extracts a supply of shell building calcium chemicals.