Crustaceans and Mollusks are animals that have shells. Most crustaceans and mollusks live in water, but some live on land.

Crustaceans are a group of animals whose skeletons are on the outside of their bodies. They live in saltwater and breathe through gills, just like fish. They have many pairs of legs, and their bodies are jointed, like a human’s elbows or knees. Crustaceans use feelers for touching, feeling and smelling.

Some crustaceans can swim, like crabs and shrimp. Some can only scuttle along the ocean floor, like the lobster. And the barnacle sticks to a hard spot and never moves at all.

Crustaceans are the most numerous animals in the oceans, but some crustaceans live in fresh water. There are about 30,500 known species of crustaceans around the world.

Some Characteristics of Crustaceans:
* A hard exoskeleton made of calcium - no internal skeleton.
* The head has two eyes, two pairs of antennae, and three mouthparts.
* A pair of green glands excrete wastes near the base of antennae.
* The abdominal segments have swimming legs)
* The tail is fan-shaped.
* The circulatory system is open; there is no heart and the "blood" is pumped by vessels into sinuses, and does not flow in a closed loop.
* The nervous system consists of a primitive central nerve cord (similar to those of an earthworm).

Some Crusteans include:

Crabs

Crayfish

Lobsters

Shrimp

Krill

Barnacles

Click here to look at pictures of real crustaceans

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Mollusks: There are over 50,000 known species of Mollusks. Most mollusks have 3 body regions: a head, a visceral mass, and a "foot." The head contains the sense organs and "brain," while the visceral mass contains the internal organs. The "foot" is the muscular lower part of the body which is in contact with the substrate.

Mollusks usually have a shell (although some do not). Mollusks have well developed body organs (nervous system, circulatory system, respiratory system, etc.) .

Mollusks with shells include:

Oysters,

Scallops

Clams

Snails