Arthropoda

__**Arthropoda**__

media type="youtube" key="MY64RV79Hr0" height="385" width="640" Grasshoppers, butterflies, beetles, ants, etc. 1,000,000 described world species
 * The arthropods constitute over 90% of the animal kingdom and are classified in the phylum Arthropoda. They are distinguished from other animals by:
 * an exoskeleton (a skeleton on the outside of the body)
 * body divided into distinct parts
 * jointed legs and appendages
 * bilateral symmetry (both sides of the body are the same) ||
 * **Class Distinctions**
 * Insects**

Spiders, scorpions, ticks, mites, etc. 65,000 described world species
 * three body regions: head, thorax, abdomen
 * six legs attached to the thorax (which has 3 segments)
 * adults with one or two pairs of wings attached to the thorax (some have none)
 * two antennae
 * lateral compound eyes || [[image:http://insected.arizona.edu/graphics/ant1.gif]] ||
 * **Arachnids**

Classes include crabs, shrimps, lobsters, barnacles, isopods etc. 44,000 described world species Centipedes. 2,800 described world species Millipedes. 10,000 described world species ||
 * two body regions: cephalothorax, abdomen
 * eight legs
 * no antennae
 * Mouth parts are chelicerae(modified appendages) which in spiders are fangs || [[image:http://insected.arizona.edu/graphics/spider1.gif]] ||
 * **Crustaceans** (technically a subphylum)
 * two body regions
 * two pairs of antennae
 * 5 or more pairs of legs
 * primarily aquatic, few terrestrial || [[image:http://insected.arizona.edu/graphics/lobster.gif]] ||
 * **Chilopods**
 * well-defined head
 * first pair of legs modified for envenomation
 * flattened top to bottom
 * one pair of legs per segment
 * one pair of antennae || [[image:http://insected.arizona.edu/graphics/chilo.gif]] ||
 * **Diplopods**
 * two pairs of legs per segments, first four segments have 1 pair legs
 * one pair of antennae
 * well-defined head