Chapter 30Arthropods

I. Features of ArthropodsA. 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 Plan1. Segmentation• Individual segments often exist only during

the larval stage• Segments fuse into three distinct regions

during developmenta. The headb. 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 ArachnidsA. Arachnid

Modificaitons• Chelicera are

modified into pincers or fangs• Two body parts

- Chephalothorax – a head and thorax fused together

- Abdomen

B. Arachnid Diversity1. 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. InsectsA. Insect Diversity• Chewing mouthparts called mandibles• Three classes

- Insecta (insects)- Diplopoda (millipedes)- Chilopoda (centipedes)

B. Insect Body Plan1. 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 Cycle1. 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 Relatives1. 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 Crustaceans1. 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