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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

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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.

Arthropods and their relatives

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

Book gills folded gills increase sa for respiration horseshoe crab

Book Gills – folded Gills increase SA for RespirationHorseshoe Crab

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.

Book lungs are characteristic of arachnids

Book Lungs are Characteristic of Arachnids

Sensory adaptations

Sensory Adaptations

  • Well developed nervous system

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

Ultravision seeing in the uv spectrum

Ultravision – Seeing in the UV Spectrum

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

Exoskeleton of chitin and muscles attach on inside

Exoskeleton of Chitin and Muscles attach on Inside

How do you grow larger if you skeleton is on the outside

How do You Grow Larger if you Skeleton is on the Outside?

Molt, or shed the outer covering

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

Chelicera fangs for example on a spider

Chelicera = Fangs, for example, on a Spider

Chelicerates include the horseshoe crab

Chelicerates Include the Horseshoe Crab

Body of arachnids

Body of Arachnids

Other members of phylum arachnida 4 pairs of walking legs

Other Members of Phylum Arachnida (4 Pairs of Walking Legs)

  • Spiders

  • Ticks and Mites

  • Scorpions

Nature says don t bug me with the colour red

Nature Says Don’t Bug Me with the Colour Red!

How nature says do not touch

How Nature Says Do Not Touch

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