Animal evolution and diversity (ecdysozoa through chordata) (ch. Two of the phyla of ecdysozoa = most animals on earth: nematoda, arthropoda. The cuticle is part of the exoskeleton: made of organic (non-mineral) material that is light and flexible, can become very tough in some groups. Ecdysozoans grow by molting the cuticle ecdysis. Strong molecular evidence for this group: protostome bilaterians. Examples: ascaris, trichinella spirallis larvae within muscle, loa loa nematode in eyeball. Tardigrada and onychophora: unsure of association to arthropoda. Live in mosses, soil, or in sediments at the bottom of lakes or the ocean. Many can survive extreme stress (freezing, high heat, radiation, outer space) Velvet worms : live in moist leaf litter, prey on small invertebrates, segmented body, limbs are not jointed, catch prey by shooting sticky slime. Cuticle is stiff, composed of protein and chitin. Open circulatory system: hemocoel cavity contains hemolymph. Higher level relationships are subjective: changing with more molecular data.