Young Brunette Girl Reveals Her Seashell Necklace And Tan Lines In The Sand On The Rocky Beach

The word "seashells" is often used to mean only the shells of marine mollusks. Marine mollusk shells that are familiar to beachcombers and thus most likely to be called "seashells" are the shells of marine species of bivalves (or clams), gastropods (or snails), scaphopods (or tusk shells), polyplacophorans (or chitons), and cephalopods (such as nautilus and spirula). These shells are very often the most commonly encountered, both in the wild, and for sale as decorative objects.
Marine species of gastropods and bivalves are more numerous than land and freshwater species, and the shells are often larger and more robust. The shells of marine species also often have more sculpture and more color, although this is by no means always the case.
In the tropical and sub-tropical areas of the planet, there are far more species of colorful, large, shallow water shelled marine mollusks than there are in the temperate zones and the regions closer to the poles.
Although there are a number of species of shelled mollusks that are quite large, there are vast numbers of extremely small species too, such as micromollusks.