Various seashellsSeashell on a beach

Discover great deals on the many top brand items available only on eBay!

Sea Shells & Barnacles

The hard, rigid outer calcium carbonate covering of certain animals is called a shell. While many animals, particularly those that live in the sea, produce exoskeletons, usually only those of mollusks are considered to be shells. more...

Aquarium CoralAquarium Coral
Aquarium DecorationsAquarium Decorations
Aquarium OrnamentsAquarium Ornaments
Other Aquarium DecorationsOther Aquarium Decorations
Plastic PlantsPlastic Plants
Rocks & GlassRocks & Glass
Sea Shells & BarnaclesSea Shells & Barnacles
Aquarium LightingAquarium Lighting
Aquarium Meters, RegulatorsAquarium Meters, Regulators
Aquarium StandsAquarium Stands
Aquariums & BowlsAquariums & Bowls
Cleaning & Water TreatmentsCleaning & Water Treatments
Crabs, Snails & Algae EatersCrabs, Snails & Algae Eaters
Filtration & HeatingFiltration & Heating
Fish FoodFish Food
Live Aquarium PlantsLive Aquarium Plants
Live Aquarium RockLive Aquarium Rock
Other Fish SuppliesOther Fish Supplies
Tropical FishTropical Fish
Guinea PigsGuinea Pigs
Other AnimalsOther Animals
Sugar GlidersSugar Gliders
Tadpoles & FrogsTadpoles & Frogs

It is sometimes erroneously claimed that shells are made of chitin, but these are unrelated materials (except for their hardness and use as a covering by animals).

The shell is usually made of nacre, an organic mixture of outer layers of horny conchiolin (a scleroprotein), followed by an intermediate layer of calcite or aragonite, and then a layer of calcium carbonate (CaCO3) in the form of platy crystals.

Nacre is secreted by the epithelial cells (formed by the ectoderm) of the mantle tissue of certain species of mollusk. Mollusk blood is rich in a liquid form of calcium. In these mollusks the calcium is concentrated out from the blood where it can crystallize as calcium carbonate. The individual crystals of each layer differ in shape and orientation. Nacre is continually deposited onto the inner surface of the animal's shell (the iridescent nacreous layer, also known as mother of pearl), both as a means to smoothen the shell itself and as a defense against parasitic organisms and damaging detritus.

When a mollusk is invaded by a parasite or is irritated by a foreign object that the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives.

Shells are very durable and outlast the otherwise soft-bodied animals that produce them by a very long time. Large amounts of shells may form sediment and become compressed into limestone. Shells that wash up on beaches are called seashells, and are collected by some enthusiasts.


[List your site here Free!]

Click to see more Sea Shells & Barnacles items at
Prices current as of last update, 12/01/23 6:57am.

Home Contact Resources Exchange Links ebay