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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.