The Arthropods
Phylum Arthropoda: protostome coelomates with segmentation but never a trochophora
most successful phylum: 1,000,000 species = 2/3 of all known species; most abundant phylum on earth
Two major innovations:
- jointed appendages: Greek arthros = joint, podus = foot higher motility, flexibility, many special modifications
- exoskeleton of chitin and protein: external skeleton, water loss reduced, protection against predators, anchor for muscle action; however, also size constraint! Requires molting
5 classes:
- Centipedes & Millipedes – Arachnids (spiders)
- Crustaceans – Insects