Arthropod Information

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)

Insects
Grasshoppers, butterflies, beetles, ants, etc. 1,000,000 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

Arachnids
Spiders, scorpions, ticks, mites, etc. 65,000 described world species

• two body regions: cephalothorax, abdomen
• eight legs
• no antennae
• Mouth parts are chelicerae(modified appendages) which in spiders are fangs

• two body regions
• two pairs of antennae
• 5 or more pairs of legs
• primarily aquatic, few terrestrial

• well-defined head
• first pair of legs modified for envenomation
• flattened top to bottom
• one pair of legs per segment
• one pair of antennae

• two pairs of legs per segments, first four segments have 1 pair legs
• one pair of antennae
• well-defined head
• usually cylindrical

The Arthropod Body Plan

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