How do sea shells grow?

Answer 1

True sea shells are seen in mollusks, which are basically sea snails of many different types.

The shell will grow over time as the animal inside adds its building material to the leading edge near the opening. This causes the shell to become longer and wider to better accommodate the growing animal inside. A mollusk shell is formed, repaired and maintained by a part of the mollusk called the mantle. Injuries to the mantle are often reflected in the shell they form. When the animal encounters harsh conditions which limit its food supply or otherwise cause it to become dormant for a while, the mantle often ceases to produce the shell substance. When conditions improve again and the mantle resumes its task, a "growth line" is produced, and the pattern and even the colors on the shell are sometimes quite different from previous colors and patterns.

The majority of shells are made of nacre, an organic mixture of outer layers of horny conchiolin (a protein), followed by an intermediate layer of calcium carbonate as either calcite or aragonite in the form of platy crystals.

Answer 2

down by the seashore?