Arthropods and their relatives
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Arthropods and Their Relatives. Characteristics Exoskeleton (external covering made of CHITIN ) Molts or sheds exoskeleton to grow Jointed appendages - Groups very often named in relation to number or type of feet.

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Arthropods and their relatives
Arthropods and Their Relatives

  • Characteristics

    • Exoskeleton (external covering made of CHITIN)

    • Molts or sheds exoskeleton to grow

    • Jointed appendages - Groups very often named in relation to number or type of feet.

    • Tend to undergo metamorphosis or pass through a number of distinct growth stages during their lives

    • Tendency toward High degree of cephalization, especially in Class Insecta


  • Relative abundance.

    • 3/4 of all known species of animals are arthropods.

    • More known species of arthropods than known species of plants and animals combined. Great diversity in form and habitat.

Major groups of arthropods
Major Groups of Arthropods

  • Subphylum Trilobita - all forms extinct (believed) perhaps some of earliest arthropods

  • Subphylum Chelicerata - First pair of appendages form chelicera or pincher-like structures used for feeding. 4 pair of walking legs, no antennae. The Arachnida is the only important parasitic group.

Major groups of arthropods1
Major Groups of Arthropods

  • Subphylum Crustacea - mostly aquatic, most have gills, two pair of antennae. Biramous appendages, meaning limbs have more than one branch. Also have mandibles. Some are parasitic but we will not cover them.

  • Subphylum Uriramia – single branch or uriramous appendages, mandibles, one pair of antennae

Major groups of arthropods2
Major Groups of Arthropods

  • Diplopoda - Millipedes - two pair of legs per body segment

  • Chilopoda - Centipedes - one pair of legs per body segment

  • Insecta - 3 pair of legs on adults, many with wings, most important group


  • Simple or gradual

    • three changes

      • egg

      • nymph

        • 3-5 instars

      • adult

    • adults and nymphs

      • eat same food


  • Complex or complete

    • four changes

      • egg

      • larva

      • pupa

      • adult

    • larvae and adults

      • eat different food

        • larvae are destructive

Fundamental external structure
Fundamental External structure

  • Insects

    • 3 body regions

      • head

      • thorax

      • abdomen

    • 3 pair legs attached to thorax

    • 1 pair antennae

    • wings usually present in adult state.

Hind Wing

Fore Wing


Simple Eye

Compound Eye

Jumping Leg





Walking Legs





Circulatory system
Circulatory System

  • Closed circulatory system

  • Well developed heart pumps blood

  • Heart is long and narrow

  • Arteries branch into blood vessels and return blood to the heart via veins – cool, just like us!


  • Recall the Nephridia in Annelids

  • The Malphigian Tubules in Arthropods collect nitrogenous wastes in the tubules from blood

  • Wastes are concentrated (like a kidney does.) Why concentrated?

  • Excreted out anus

Respiratory system
Respiratory System

  • Gills or lungs, as you’ll see on the next slide 

  • Organism is too large to rely on surface area. That is, the internal volume is too great to be supplied with oxygen from a minimal SA.

Sensory adaptations
Sensory Adaptations

  • Well developed nervous system

  • Compound eyes with many lenses give Mosaic Vision or multi-images

The compound eye
The Compound Eye

Each crystalline eye generates an image. All images together generate a mosaic effect

Simple eye ocelli
Simple Eye (Ocelli)

  • Do not form the picture

  • Just gather light

  • Tell whether it’s light or dark

External structure of subphylum chelicerata class arachnae
External structure of Subphylum Chelicerata, Class Arachnae

  • Chelicerates have specialized mouthparts called chelicerae – think of the hooked grabbers!

  • Arachnids (spiders and mites)

    • 2 body regions

      • Cephalothorax

      • abdomen

    • usually 4 pair legs

    • no wings

    • no antennae