As nautilus grows, each shell is sealed off -> gas filled. Lecture 14: arthropods (cid:894)i(cid:374)sects, spiders, crustacea, (cid:373)illipedes, (cid:895) 4 major sub-phyla & one important extinct group. Enormous number of fosilised animals found in the burgess shale in canadian rocky mountains (cambrian explosion) -> 510 million years old. Lobster: fused head & thorax (cephalothorax), segmented body areas. Existed from early cambrian (530 mya) until the end of the permian (250 mya), started declining after end of the devonian (360 mya) Extinction of trilobites coincides with the evolution of jaws in fish (introduction of predators/competition?) Modified mouthparts: chelicerae -> sharp mouthparts for bites (injection of venom?) Mostly omnivorous; some filter feeders (barnacles, bivalves); few carnivorous. Mostly terrestrial marine environment is already colonized by crustacea. Wing (cid:373)odifi(cid:272)atio(cid:374) of e(cid:454)oskeleto(cid:374) stre(cid:374)gthe(cid:374)ed (cid:271)(cid:455) (cid:858)vei(cid:374)s(cid:859) Stoneflies: early wings aid locomotion across water surface. Chewing, sucking, sponging, siphoning: why arthropods are successful, exoskeleton. Hard plates separated by soft membranes -> movement.