Arthropods Have Exoskeletons & Joints MOST INVERTEBRATES ARE ARTHROPODS Most common type of invertebrate: arthropod = invertebrate with segmented body covered by hard outer skeleton; many pairs of legs; insects, crustaceans & arachnids are arthropods INSECTS ARE SIX-LEGGED ARTHROPODS CRUSTACEANS LIVE IN WATER AND ON LAND ARACHNIDS ARE EIGHT-LEGGED ARTHROPODS MILLIPEDES AND CENTIPEDES ARE ARTHROPODS

Arthropods: exoskeletons Exoskeleton made of hard “chitin”, like suit of armor protecting it & keeping it moist (if on land). Joints (where chitin is thin & flexible) allow for movement; muscles attach around joints for this. 3 main body parts: Head, Thorax, & abdomen Exoskeleton doesn’t grow, it molts (sheds old one and grows new one); this is dangerous time because new one stays soft for awhile.

Insect: 6 legged arthropods Arthropods have well-developed nervous & digestive systems; open circulatory system with blood moving into body without blood vessels; reproduce sexually; either male or female parts. As adults have 3 body segments, pair of antennae, 6 legs attached to thorax. If on land, have spiracles (openings in exoskeleton to bring in oxygen). Many can blend in to environment, or have wings. Many are herbivores with designs for specific plants to eat (butterfly has tube to reach nectar) Some are social insects (bee, termite, ant) living in groups; work together to get food, maintain nest & care for offspring; usually just one female (queen) lays eggs.

Insect=most common arthropod All insects reproduce sexually; female lays many eggs(often with protective hard covering to keep from drying out) Insects undergo metamorphosis(3 stages of change): Egg hatches into Larva= spends its time eating; Pupa=second stage, insect body develops inside of protective casing; Adult= final stage, insect able to reproduce now Some insects skip some of the metamorphic stages Many larval stages are common (caterpillar, inchworm); often larva are very different (mosquito larva live in water & feed on algae, pupa form on water surface & adult flies off to feed on blood of animals & lay eggs in water again).

Crustacean Arthropods Most live in water; many used as food source in important food webs & by humans. 3 or more pairs of legs & 2 pair sensory antennae Most have heart but no blood vessels like other arthropods May eat plants/small animals, or remains of other organisms (barnacle is filter feeder) Barnacle larva is free swimming, then attaches as adult to hard surface (rock/boat/mollusk shell) & uses its tentacles to grab food from surrounding water.

Arachnid- 8 legged arthropod Spiders, mites, ticks & scorpions are arachnids. Exoskeleton, jointed limbs, segmented bodies (like all arthropods) but also have 4 pairs of legs and only 2 body segments; no antennae Some are parasites(tics,chigger mites), others are predators (spiders & scorpions). These get prey by stinging, biting or injecting venom. Most arachnids are spiders. Make strong silk to form webs to capture food. Spinnerets at rear of abdomen spins strands of silk into web. Some arachnids have spiracles to get oxygen, while others (some spiders) have “book lungs” (moist folded pockets within abdomen).

Millipede & Centipede Arthropods Both have long, segmented bodies with many legs. Reproduce sexually, hatch from eggs. Millipedes have 2 pair of walking legs on each body segment; move slowly & eat decaying leaves & plant matter; may emit foul odor if disturbed which may harm predators. Centipedes move quickly, have 1 pair of legs per segment, have antennae & jaw-like mouthparts. Many have pincers on rearmost segment. Are predators that can paralyze prey.