Sea Shells

Mollusks first evolved in the sea and have been adapting to its changing ecological niches for nearly 600 million years. So it is not surprising that marine species exhibit the phylum‘s greatest diversity. Mollusca in general exhibit more morphological diversity than any other phylum, including arthropods. The vast difference between the giant squid and microscopic nuculid clams is unmatched in the animal kingdom.

While many sea animals produce exoskeletons, usually only those of molluscs are normally considered to be "sea shells". The majority of shell-forming molluscs belong to the classes Gastropoda or Bivalvia. Three other shell-bearing classes are Scaphopoda , Polyplacophora and Monoplacophora. Some species of Cephalopoda also build shells, including the primitive Nautilus order which produces the famous "chambered Nautilus" shell; although some taxa of cephalopods such as octopi and squid only form small internal shells.

Some sea shells are carnivores, some are strict vegetarians, others are scavengers or parasites or commensals; the bivalves, for the most part are sedentary filter feeders, but some are predacious. Marine mollusks burrow, creep, tunnel, float or swim. They make their homes in mud, sand, silt, coral grit, rock, shell, tidal pool or grass.