28.2

Arachnids Class Arachnida Spiders (largest group), scorpions, mites, ticks Two body regions Cephalothorax Abdomen Chelicerae: appendages modified into pincers or fangs to stab & paralyze prey

Arachnids: Nutrition Use pincers to hold food Fangs inject poison into prey Extracellular digestion liquefies internal organs of prey Spider sucks up liquefied food Pedipalps: handling food & sensing Grab prey Males: can carry sperm during reproduction

Arachnids: Nutrition Four other appendages Modified as legs for locomotion NO ANTENNAE

Silk Not all spiders make webs Silk is secreted by silk glands in the abdomen Spun into threads by spinnerets

Ticks, Mites, & Scorpions One body section: head, thorax, abdomen fused Ticks Feed on blood from reptiles, birds, & mammals Expand after meal Can spread disease

Ticks, Mites, & Scorpions Mites Too small to see Chiggers bite can be felt Scorpions Long tail with venomous stinger at tip Live in warm, dry climates Eat insects & spiders Use poison to paralyze prey

Crustaceans Class Crustacea Aquatic Gas exchange through gills 2 pairs of antennae for sensing Mandibles for crushing food Open/close from side to side

Crustaceans 2 compound eyes on movable stalks 5 pairs of walking legs (swimmerets) 1 st pair (chelipeds) modified as claws for defense 2-3 body sections Crabs, lobsters, shrimp, water fleas

Centipedes Class Chilopoda Flattened body with many tiny, jointed legs Carnivorous: eat snails, slugs, worms Bite hurts humans 1 pair of legs per segment

Millipedes Class Diplopoda Eat mostly plants & dead material on damp forest floor Do NOT bite Spray obnoxious- smelling fluids from defensive stink glands 2 pairs of legs per segment

Horseshoe Crabs Class Merostomata Unchanged since Cambrian period About 500 million years ago Exoskeleton Search on land/muddy ocean floor for seaweed, worms, mollusks Lay eggs on land

Insects Class Insecta Largest group of arthropods Reproduction Internal fertilization Mate only once in life time Lay a large number of eggs

Complete Metamorphosis Four stages: Egg Larva: free-living, wormlike stage Molts several times Pupa: reorganization of tissues from larvae to adult stage Does not feed or move Adult: wings first appear 90% of insects go through complete met. Larvae & adults do not compete for the same food

Incomplete Metamorphosis Three stages: Egg Nymph: lack some appendages Can not reproduce Wings begin to form Eats & grows, molts several times Internal reproductive system begins to develop Adult P. 729—shows cycles on bottom