main characteristics - protostomes, largest animal phylum
- level of organization - organ systems
- body symmetry - bilateral
- alimentary structures - 2-hole tube
- triploblastic
- hemocoelomate - has blood cavity (hemocoel)
- chitin exoskeleton
- shed/renewed as organisms grow
- jointed/paired appendages
- much segmentation
- tagmosis - fusion of segments into functional units
- open circulatory system
- respiratory system w/ spiracles, tracheae, book lungs/gills
- sexual, dioecious reproduction (sometimes parthenogenic)
subphylum Chelicerata - have chelicerae for stinging, absorption of food
- pedipalps - used to sense surroundings (sort of like antennae)
- body segments - cephalothorax, abdomen
- book gills/lungs, tracheae
- Class Merostomata - Horseshoe crabs
- Class Arachnida - spiders, scorpions, ticks, mites
subphylum Crustacea - mandibles for chewing instead of chelicerae
- biramous - double-branched appendages
- compound eyes (multiple lenses)
- gills, book lungs
- 2 pair of antennae
- Class Malacostraca - shrimp, crabs, crayfish, krill
- Class Branchiopoda (water fleas), Copepoda (Copepods)
subphylum Uniramia - uniramous (single branch appendages)
- mandibles
- 1 pair of antennae
- Class Chilopoda - centipedes
- carnivores
- 1 pair of legs per segment
- Class Diplopoda - millipedes
- herbivores
- 2 pairs of legs per segment
- Class Insecta (Hexapoda) - insects
- 6 legs
- head, thorax, abdomen
- modified mouthparts
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