1. The Arthropods Arthro = jointed, Pod = foot
Phylum Arthropoda
The Arthropods
Arthro = jointed, Pod = foot
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2. Largest animal phylum containing more than 3x the number of all other animal species combined.
More than 750,000 species identified (in blue).
Also has the most biomass of any group.
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3. Phylum Arthropoda General characteristics: Segmented body
Tough exoskeleton composed of chitin
Jointed appendages.

4. Main Groups of Arthropods
Arthropods are classified based on the number and structure of their body segments and appendages – particularly their mouth parts
Subphylum Crustaceans – crabs, shrimp, lobsters, pill bug, and crayfishes
Subphylum Chelicerates – horseshoe crabs and arachnids (spiders, ticks, scorpions)
Subphylum Uniramia – insects, millipedes, and centipedes

5. Arthropod Digestive System
Arthropods feed on a variety of things: herbivores, carnivores, detritivores (detritus = dead leaves, etc.), filter feeders, and parasites.
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6. Arthropod Excretion (Urination)
Malphigian Tubules are used to dispose of nitrogenous wastes. These thin, tubelike organs take N2 from blood and add it to feces.
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7. Arthropod Circulation
Open Circulation – blood flows from heart to ends of vessels then out into an open area called a sinus. Eventually the blood flows back into the vessels through pores called ostia.
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8. Arthropod Respiration
Most terrestrial arthropods breathe through tracheal tubes that extend throughout the body. Air enters and leaves the body through openings called spiracles located along the length of the animal.
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9. Arthropod Respiration
Others such as spiders respire using “book lungs” that have layers of respiratory tissue.
Aquatic arthropods breathe using gills.
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10. Arthropod Nervous System
Arthropods exhibit cephalization having a brain and central nerve cord
How is the location of the nerve cord different than in humans?

11. Arthropod Reproductive Organs
Sexes are separate.
Female Male
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12. Arthropod Fertilization
Aquatic Arthropods reproduce sexually using both external and internal fertilization.
Terrestrial Arthropods reproduce sexually using internal fertilization.
Only a few species bear live young. Most females lay fertilized eggs.

13. Arthropod Development
Arthropods undergo a period of molting in which they shed their exoskeleton and grow a new one
Since the animal has no protection at the time of molting they will often hide themselves

14. Subphylum Crustaceans
Have several mouthparts, three body sections that may be fused, 5 or more pairs of legs, and two pairs of antennae.
Most are aquatic.
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15. Subphylum Chelicerates
Have mouthparts called chelicarae, two body sections (cephalothorax and abdomen), 4-5 pairs of legs, and lack antennae.
Most are terrestrial.
HORSESHOE CRABS have the body structure more like a spider with a hard plated shell like a crab – they can be as big as a frying pan!

16. Subphylum Chelicerates
SPIDERS: all produce silk, but not all produce webs.
MITES & TICKS: small and usually parasitic. Chiggers, mange, and scabies mites cause itching painful rashes in humans and other mammals. Ticks spread Lyme disease and Rocky Mountain spotted fever.
SCORPIANS: have a venomous stinger than can paralyze and kill prey!

17. Subphylum Uniramia
CENTIPEDES: 15 to 170 pairs of legs – typically one set of legs per body segment
Centipedes are carnivorous and use venomous claws to catch arthropods, earthworms, toads, small snakes, and even mice!
Centipedes lose moisture easily so are limited to dark, damp places.

18. Subphylum Uniramia
MILLIPEDES: more legs than centipedes. Typically two sets of legs per body segment
Feed on dead and decaying plant material
Millipedes roll into a ball when startled

19. Subphylum Uniramia Characteristics:
INSECTS: These animals have the greatest impact on the activities of the planet!
Characteristics:
Exoskeleton
Body is divided into three parts (head, thorax, and abdomen)
Three pairs of legs (jointed appendages) are attached to the thorax.

20. Insect Metamorphosis Morph = shape/form
Metamorphosis – the process of changing shape or form
Incomplete Metamorphosis: the young look a lot like the adult and are called nymphs – they mature into adults as they develop wings and sexual organs.
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21. Insect Metamorphosis
Complete Metamorphosis: young larvae look nothing like adult and even feed in different ways. The young molt several times until finally molting into a pupa in which the larva changes into an adult.
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