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Arthropods. ARTHROPODS 1 million known species of arthropods. May be up to 30 million species in the world’s tropical rain forests. Two out of three animals living on earth are arthropods. Phylum Arthropoda Arthron- means joint pous- means foot

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  • 1 million known species of arthropods.
  • May be up to 30 million species in the world’s tropical rain forests. Two out of three animals living on earth are arthropods.
Phylum Arthropoda
  • Arthron- means joint
  • pous- means foot
  • Typical arthropod: an invertebrate with bilateral symmetry, a coelom, an exoskeleton, jointed appendages, an open circulatory system and complex social behavior.
Arthropods include: insects, centipeds, millipeds, spiders, ticks, scorpions, mites, lobsters, shrimp, crabs, and crayfish.
  • Evolutionary success due to jointed appendages and exoskeleton.
Jointed appendages: most recognizable feature. Allow for more powerful movements and allows appendages to be used for:
    • 1)walking,
    • 2)sensing
    • 3) feeding
    • 4) mating.

***Appendage may be a leg or an antenna.

Exoskeleton – Hard, thick outer covering made of protein and chitin. It may be one continuous covering or it is made of separate plates held together by hinges.
  • Provides: protection and support for internal tissues
    • protects against water loss
    • provides places for muscle attachment
    • Exoskeletons are heavy - some have adapted to their habitats by developing thinner, lightweight exoskeleton. However, this provides less protection.
Molting – periodic shedding of exoskeleton
    • allows the animal to grow larger;
    • 4 to 7 times in their life
    • during molting animal is vulnerable to predators
Process of Molting:
    • animal contracts muscles in the rear part of its body, forcing blood forward.
    • The forward part of the body swells, causing the old exoskeleton to split open.
    • The animal then wigglesout.
  • Less segmented than worms; the body segments have become fused into 1-3 body sections
    • 1) HEAD
    • 2) THORAX
    • 3) ABDOMEN

Some arthropods have the head and thorax fused to form a cephalothorax

Efficient gas exchange
  • Arthropods are generally quick, active animals. They crawl, run, climb, dig, swim, and fly. Some flies beat their wings 1000 times per second. Oxygen delivery to cells must be quick.
3 Types of Respiratory Structures
  • 1. gills – aquatic (Ex. Crabs)
    • large surface area enables a large amount of blood-rich tissue to be exposed to water containing oxygen.

2.tracheal tubes – land (most insects)

    • most insects
    • branching network of hollow air passages that carry air throughout body; air enters and leaves through openings on the thorax and abdomen called spiracles.
3. book lungs – land
    • Spiders
    • are air filled, folded membranes that

contain leaf-like plates

(looks like pages in a book) which increase the surface area of tissues exposed to air.

Arthropods have acute senses
  • Movement, sound, or chemicals can be detected by antennae. Antenna are also used for communication, detect pheromones. Example ants use it for scent trails and for mating.
Acute vision – most have

one pair of large compound

eyes and 3 to 8 simple eyes.

  • Simple eye – visual structure with only 1 lens, used for detecting light.

Side eyes: pick up movement

Middle front: sharp images, some color

Side front: judge distances

Compound eye – many lenses that register light from one area of the total field of view; can detect slight motion of prey, mates, or predators; can see colors, but image is fuzzy.
  • Nervous system – well developed; consists of
  • 1) ventral nerve cord
  • 2) anterior brain
  • 3) several ganglia (nerve & tissue cells)

circulatory (yellow),

digestive (green),

nervous (blue) systems.

Open Circulatory system – one or more hearts; blood flows out of vessels, bathes the tissue, returns to heart through open body spaces.
  • Complex Digestive System
  • 1) mouth – contain a variety of jaws called mandibles; mouthparts are adapted for holding, chewing, sucking or biting, this enables them to fit a variety of niches.

Sand flies feed by drawing blood

  • Butterflies and moths use a rolled-up sucking tube

Sponging tongue of housefly uses saliva to digest food

Most terrestrial arthropods excrete wastes through Malpighian tubules. They are located in the abdomen, attached to and empty into the intestine
  • Muscular System – attached to exoskeleton
Reproductive System – most species have male and females that reproduce sexually
  • Terrestrial arthropods – internal fertilization
  • Aquatic arthropods - external fertilization
Some species are hermaphrodites (animals w/both male and female organs).
  • Some species are asexual. Reproducing through a process called parthenogenesis (organism develops from an unfertilized egg).
  • Found in a wide variety of habitats due to the variety of adaptations they have for obtaining and digesting food. Some are consumers and others are parasites (some lay eggs on the larvae of other insects).

Beneficial to humans

  • 1) pollinate flowering trees and crop plants
  • 2) wax
  • 3) silk
  • 4) provide alternatives (ladybird beetles) to chemical
  • 5) control of other insects
Research on arthropods has led to advances in the fields of genetics, evolution, and biochemistry. From crab shells, scientists have made artificial skin, surgical sutures, and anti-fungal medication.

But, they can also be detrimental to humans.

  • 1) Spread diseases to plants and animals (West Nile, malaria, yellow fever, Lyme’s disease)
  • 2) Eat crops.