Ecdysozoans – animals with exoskeletons or
tough cuticle, which molts to allow growth
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
Ecdysozoans with unjointed legs
• Cuticle contains chitin, so these phyla are
related to the arthropods.
• Onychophora
Tardigrada
(“water bears”)
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
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.
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
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
Phylum Chelicerata
• Spiders, mites, ticks, and scorpions
• Often with four pairs of walking legs
• The most important class is the Arachnida
(spiders)