Most crustaceans live in water, but some live on land. Crustaceans are the most numerous animals in the oceans, but some crustaceans live on 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 compound eyes, two pairs of antennae, and three pairs of mouthparts.
• A pair of green glands excrete wastes near the base of antennae.
• The abdominal segments have swimmerets (swimming legs)
• The sexes are separate. Eggs are attached to the swimmerets (swimming legs) of the female. The first pair is enlarged in the male (it is used to pass sperm to the female).
• The tail is fan-shaped, and ends in uropods and a telson.
• 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 ventral nerve cord and ganglia system (similar to those of an earthworm).

Classification: Kingdom Animalia, Phylum Arthropoda, Subphylum Crustacea, Classes:

• Class Cephalocarida (primitive, shrimp-like, discovered in 1955) - 9 species
• Class Branchiopoda (with flattened gill-carrying appendages) - about 800 species, including brine shrimp, fairy shrimp, water fleas, etc.
• Class Malacostraca - 18000 species, including lobsters, shrimp, crabs, woodlice, isopods, amphipods, krill, etc.
• Class Maxillopoda (ostracods, copepods, barnacles)
• Class Remipedia (primitive crustaceans discovered in submerged caves by Jill Yager in 1980)

Some crustaceans include:

Copepod Copepods are tiny crustaceans from fresh and salt water.

Crab A crab is an animal with a crusty shell. There are marine and land species of crabs.

Crayfish Freshwater crustaceans with four pairs of walking legs.

Crayfish Diagram: Label Me! Label the external anatomy of the crayfish. Answers

Fiddler Crab Diagram: Label Me! Label the external anatomy of the fiddler crab. Answers

Hermit Crab Hermit crabs are crabs that lack a hard shell; they use a discarded shell for protection.

Hermit Crab Diagram: Label Me! Label the external anatomy of the hermit crab both in its shell and out of it. Answers

Krill Small crustaceans that are eaten by many animals, including baleen whales.

Lobster A hard-shelled marine invertebrate with 10 jointed legs.

Pill Bug The pill bug (also called the roly-poly bug) is a small isopod that curls into an armored ball when it is threatened.

Shrimp Shrimp are small, bottom-dwelling crustaceans with a translucent exoskeleton.

Trilobite Trilobites are extinct marine crustaceans that lived in the seas from about 540 to 245 million years ago.

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