Arthropod Information

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What is an arthrpod?

The arthropods constitute over 90% of the animal kingdom and are classified in the phylum Arthropoda. They are distinguished from other animals by:

  • an exoskeleton (a skeleton on the outside of the body)
  • body divided into distinct parts
  • jointed legs and appendages
  • bilateral symmetry (both sides of the body are the same)
Class Distinctions

Insects
Grasshoppers, butterflies, beetles, ants, etc. 1,000,000 described world species

  • three body regions: head, thorax, abdomen
  • six legs attached to the thorax (which has 3 segments)
  • adults with one or two pairs of wings attached to the thorax (some have none)
  • two antennae
  • lateral compound eyes

Arachnids
Spiders, scorpions, ticks, mites, etc. 65,000 described world species

  • two body regions: cephalothorax, abdomen
  • eight legs
  • no antennae
  • Mouth parts are chelicerae(modified appendages) which in spiders are fangs
Crustaceans (technically a subphylum)
Classes include crabs, shrimps, lobsters, barnacles, isopods etc. 44,000 described world species

  • two body regions
  • two pairs of antennae
  • 5 or more pairs of legs
  • primarily aquatic, few terrestrial
Chilopods
Centipedes. 2,800 described world species

  • well-defined head
  • first pair of legs modified for envenomation
  • flattened top to bottom
  • one pair of legs per segment
  • one pair of antennae
Diplopods
Millipedes. 10,000 described world species

  • two pairs of legs per segments, first four segments have 1 pair legs
  • one pair of antennae
  • well-defined head
  • usually cylindrical

The Arthropod Body Plan

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