Ecdysozoans – animals with exoskeletons or tough cuticle, which molts to allow growth

1. Ecdysozoans – animals with exoskeletons or tough cuticle, which molts to allow growth

2. Nematoda - roundworms • pseudocoelomate • not an exoskeleton as such, but a thick cuticle that is shed as the animal grows. • Live in waters, soils, and as parasites of both animals and plants. • One of the most diverse groups of organisms on earth. • 25,000 species described • Perhaps millions still unknown

4. Ecdysozoans with unjointed legs • Cuticle contains chitin, so these phyla are related to the arthropods. • Onychophora Tardigrada (“water bears”)

5. Arthropods • Rigid exoskeleton • Jointed legs • “Arthropoda” was formerly regarded as a phylum, but is now seen as a group of 4 related phyla • Crustacea – shrimp, lobsters, crabs • Hexapoda – includes class Insecta (insects) • Myriopoda: centipedes and millipedes • Chelicerata – spiders, mites, lice, scorpions

6. Crustacea • 3 regions: Head, thorax, and abdomen • Multiple segments in thorax and abdomen • 5 pairs of appendages on head • One pair of appendages on each thoracic or abdominal segment • Appendages specialized for various uses: antennae, jaws, legs, swimmerettes, etc.

8. Phylum Hexapoda • One main class, the insects (Insecta) • Head, thorax, and abdomen • 6 legs on thorax • Some important orders (see pictures P. 649): • Odonata: Dragonflies • Orthoptera: Crickets, grasshoppers, roaches • Coleoptera: Beetles • Diptera: Flies • Lepidoptera: Butterflies, moths • Hymenoptera: Bees, wasps, ants

9. Phylum Miriapoda • Centipedes and millipedes • Many approximately equal body segments • Legs on every segment • One pair per segment in centipedes • Two pairs per segment in millipedes

10. Phylum Chelicerata • Spiders, mites, ticks, and scorpions • Often with four pairs of walking legs • The most important class is the Arachnida (spiders)