Phylum Arthropoda

The ArthropodsArthro = jointed, Pod = foot

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•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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Phylum Arthropoda

• General characteristics:

1.Segmented body2.Tough exoskeleton

composed of chitin3.Jointed

appendages.

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

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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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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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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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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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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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?

Arthropod Reproductive Organs

• Sexes are separate.Female Male

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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.

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

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.Source

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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!

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!

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.

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

Subphylum Uniramia

Characteristics:1. Exoskeleton2. Body is divided into

three parts (head, thorax, and abdomen)

3. Three pairs of legs (jointed appendages) are attached to the thorax.

INSECTS: These animals have the greatest impact on the activities of the planet!

Insect Metamorphosis

Morph = shape/formMetamorphosis – 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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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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