A shell is a hard, rigid outer layer, which has evolved in a very wide variety of different
animals, including
mollusks,
sea urchins,
crustaceans,
turtles and
tortoises,
armadillos, etc. Scientific names for this type of structure include
exoskeleton,
armour,
test,
carapace, and
peltidium. The shells that are perhaps most familiar and most commonly encountered, both in the wild and for sale as decorative objects, are
seashells, or more precisely, the external shells of
marine mollusks (also spelled molluscs). These are usually primarily composed of
calcium carbonate, which can take different crystalline forms, one being
nacre otherwise known as mother of pearl.
See more at Wikipedia.org...
Free Download Now!
