Chapter 30 Arthropods

I. Features of Arthropods A. Jointed Appendages Appendages are structures that extend from the arthropod’s body wall They have joints that bend Include: - Legs for walking - Antennae for sensing the environment - Mouthparts for chewing food

B. Arthropod Diversity About 900,000 species 2 groups - Arthropods with jaws - Arthropods with fangs or pincers

C. Arthropod Body Plan 1. Segmentation Individual segments often exist only during the larval stage Segments fuse into three distinct regions during development a. The head b. The thorax (midbody region) c. Abdomen

2. Compound Eyes Eyes composed of thousands of individual visual units, each with its own lens and retina Some arthropods have single-lens eyes that only distinguish light form dark - Function as horizon detects for stabilization during flight

3. Exoskeleton Composed of chitin Thin and flexible where the joints are located Muscles attached to the exoskeleton can pull against it, causing the joints to bend Provides protection and helps to prevent water loss

4. Molting An exoskeleton cannot grow larger so the arthropod cannot simply grow bigger In a process called molting, arthropods shed and discard their exoskeletons periodically

5. Respiration A network of fine tubes called tracheae Air enters through spiracles and passes into the tracheae, delivering oxygen throughout the body

6. Excretion Malpighian tubes extend from the gut and are bathed by blood Dissolved particles move through the tubules and into the gut Water, valuable ions, and metabolites are reabsorbed into the body tissues Metabolic wastes are excreted

II. Spiders and Other Arachnids A. Arachnid Modificaitons Chelicera are modified into pincers or fangs Two body parts - Chephalothorax – a head and thorax fused together - Abdomen

B. Arachnid Diversity 1. Spiders Poison glands secrete a toxin through their fangs The toxin kills or paralyzes the prey Enzymes digest the prey’s tissues allowing the spider to suck up liquid fluid

Only two species of spiders living in the U.S. are dangerous to humans - The black widow and brown recluse Most spiders can secrete sticky strands of silk from appendages called spinnerets

2. Scorpions Long, slender, segmented abdomens Venomous, posterior stinger used to stun their prey Pedipalps used for seizing food and during sexual reproduction

3. Mites Chiggers and ticks Single, unsegmented body Lyme disease can be spread by infected deer ticks

III. Insects A. Insect Diversity Chewing mouthparts called mandibles Three classes - Insecta (insects) - Diplopoda (millipedes) - Chilopoda (centipedes)

B. Insect Body Plan 1. Head Mandibles and mouthparts are adapted for eating different foods Compound eyes Antennae

2. Thorax Composed of three fused segments Three pairs of jointed walking legs Some have one or two pairs of wings 3. Abdomen 9 to 11 segments

C. Insect Life Cycle 1. Complete Metamorphosis A wingless, wormlike larva encloses itself within a protective capsule and passes through a pupa stage, in which it changes into an adult Larvae and adults exploit different habitats and food sources, which decreases competition and increases survival

2. Incomplete Metamorphosis An egg hatches into a juvenile, or nymph, a small, wingless adult After several molts, the nymph developed into an adult

D. Flight Allowed insects to reach previously inaccessible food sources and to escape quickly from danger Composed entirely of chitin Have a network of tubes called veins that carry air In most insects only one pair of wings is functional for flight - Other set serves as protection or stability during flight

E. Social Insects Highly organized societies of genetically related individuals Division of labor with different roles, or castes - Determined by heredity, diet, hormones, and pheromones Workers and soldier are sterile - Reproduction is a function only of the queen and king

F. Insect Relatives 1. Centipedes One pair of legs per segment Up to 173 segments carnivores

2. Millipedes Two pairs of legs on most segments 11 to 100 segments Herbivores

IV. Crustaceans “Insects of the sea” Crabs, lobsters, crayfish, shrimps, barnacles, water fleas, and pill bugs Distinctive larval form called a nauplius with three pairs of branched appendages

A. Terrestrial Crustaceans Pill bugs and sow bugs Live in leafy ground litter Land crabs live in damp areas - Life cycle tied to the ocean, where the larvae live until maturity

B. Aquatic Crustaceans 1. Decapods Shrimps, lobsters, and crabs Freshwater crayfish Five pairs of legs Cephalothorax covered by a protective carapace

One anterior pair of legs are modified into large pincers called chelipeds Swimmerets are attached to the underside of the abdomen Telson, or tail spine

2. Sessile Crustaceans Barnacles are sessile as adults Hard plates that can open and close protect the barnacle’s body Extend jointed appendages through the open plates to stir food into the barnacles’ mouth hermaphrodites