5.4. ARTHROPODS

5.4. ARTHROPODS

1. What are they like?

   • They have bilateral simmetry
   • They have exoskeleton
   • They have jointed appendages (legs, mandibles, antennae,...)
   • Their body can be divided into...
     • 1. A head, a thorax and an abdomen
     • 2. A cephalothorax and an abdomen
     • 3. A head and a trunk
   • Respiration
     • Aquatic by gills
     • Terrestrial by tracheae
   • They are oviparous (lay eggs)

2. Types

   • A) CHELICERATE
     • They have chelicerae next to their mouths
     • ARACHNIDS (spiders, scorpions and mites)
       • terrestrial and carnivores
       • Body: a cephalothorax and an abdomen
       • 8 legs (four pairs)
       • appendages: 2 pedipalps (pinzers to hold their prey)
   • B) MANDIBULATE
     • They have mandibles next to their mouths.
     • MYRIAPODS (centipedes and milipedes)
       • They are terrestrial and carnivorous or herbivorous
       • Body: a head and a trunk with many rings.
       • They have two antennae
       • One or two pairs of legs for each ring
     • CRUSTACEANS (crabs, praws and lobsters)
       • They are aquatic and carnivorous
       • Body: a cephalothorax and an abdomen
       • They have a hard exoskeleton
       • They have two antennae
       • 10 or more legs
       • They have a pair of compound eyes
     • INSECTS (grasshoppers, dragon-fly, fleas, louse, crickets, butterflies, beetles and flies)
       • They are terrestrial and can be carnivores, herbivores, scavengers or parasites
       • Body: a head, thorax and an abdomen
       • They have two antennae
       • 6 legs (three pairs) and two pairs of wings
       • They have a pair of compound eyes and a number of simple eyes

3. Metamorphosis

   • Gradual or incomplete
     • e.g. grasshopper
     • sequence: egg--> hatching--> nymph--> grow and moltings--> adult
   • Complete
     • e.g. butterfly
     • sequence: egg--> caterpillar (larva) --> grow and moltings-->pupa--> adult--> adult laying eggs

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