-The exoskeleton is made up of chitin and protein. a. Provides protection b. Provides points of attachment for the muscles that move appendages -The animal must molt (ecdysis) its old exoskeleton if it outgrows it. -Well-developed eyes, olfactory receptors, and antennae for touch and smell (most at the anterior end = cephalization). -Open circulatory system: Hemolymph (the word “blood” is reserved for a closed circulatory system) is pumped from the heart into spaces surrounding tissue and organs.

-Respiratory by gills, book lungs, and trachea.

-The arthropods came from 4 evolutionary lineages: 1. Trilobites (extinct) 2. Chelicerates (horseshoe crab, scorpions, ticks, and spiders) 3. Uniramians (centipedes, millipedes, and insects) 4. Crustaceans (crabs, lobsters, shrimp, barnacles)

Scientists now want to separate these lineages into different phylums: Phylum Trilobita, Phylum Chelicerata, Phylum Uniramia, Phylum Crustacea

-Some major classes in phylum arthropods: Arachnids: Ex. Spiders, scorpions, ticks, mites Body with 1 or 2 main parts, six pairs of appendages (Chelicerae, pedipalps, and 4 pairs of walking legs); mostly terrestrial.

-Diplopods: Ex. Millipedes Body with distinct head bearing antennae and chewing mouthparts, segmented body with two pairs of walking legs per segment; terrestrial and herbivorous.

-Chilopods: Ex. Centipedes Body with distinct head bearing large antennae and 3 pairs of mouthparts; appendages of first body segment modified as poison claws; body segments bear 1 pair of walking legs each; terrestrial; carnivorous.

-Insecta: Ex. Insects Body divided into head, thorax, and abdomen; antennae present; mouthparts modified for chewing, sucking, or lapping; usually with two pairs of wings and three pairs of legs; mostly terresterial.

-Entomology: study of insects -Flight is one of the great successes of insects.  Dragonflies were among the first insects to fly.

-Insects have a complete digestive system. -Open circulatory system (hemolymph) -Metabolic wastes removed from the hemolymph via the excretory organs called Malpighian tubules. -Gas exchange via the the trachael system open to the outside through spiracles (pores).

-Nervous system consists of a pair of ventral nerve cords that meet in the head, to form the cerebral ganglion (brain).

Many insects undergo metamorphosis.  Incomplete metamorphosis (Ex. Immature grasshoppers are small and molt until finally reaching adult size.)  Complete metamorphosis (Ex. Maggot  Fly Grub  Dragonfly Catepillar  Butterfly/Moth)

-Reproduce sexually with separate male and female individuals. The sexes recognize each other by advertising with bright colors (butterflies), sound (crickets), or odors (moths). Fertilization is internal. -Crustaceans: Ex. Crabs, lobsters, and shrimp. Two pairs of antennae, three or more pairs of appendages. Walking legs in the thorax, and abdomen. Appendages can be regenerated if lost.