18.11 Arthropods are segmented animals with jointed appendages and an exoskeleton –Various adaptations have made arthropods the most successful animals on Earth Jointed appendages adapted for different functions Exoskeleton: external skeleton that protects and provides attachment points for muscles Distinct groups of segments: head, thorax, abdomen Open circulatory system

LE 18-11a Cephalothorax Abdomen HeadThorax Antennae (sensory reception) Head Pincer (defense) Mouthparts (feeding) Walking legs Swimming appendages

–Chelicerates Horseshoe crabs Arachnids, such as spiders, scorpions, mites, and ticks Most live on land and are carnivores –Millipedes and centipedes Have similar segments over most of body Segments bear two pairs (millipedes) or one pair (centipedes) of legs

–Crustaceans Nearly all are aquatic Include lobsters, crabs, shrimps, barnacles, small copepods, and krill

18.12 Insects are the most diverse group of organisms –Insects have a number of common features Three-part body consisting of head, thorax, and abdomen –Head usually has antennae and eyes Mouthparts specialized for particular kinds of eating Three sets of legs One or two pairs of wings (most, but not all)

LE 18-12a HeadThorax Hindwing Antenna Eye Mouthparts Abdomen Forewing

18.13 Echinoderms have spiny skin, an endoskeleton, and a water vascular system for movement –Echinoderms, phylum Echinodermata, are slow-moving or sessile marine animals Include organisms such as sea stars, sand dollars, and sea urchins Adults are radially symmetrical External bumps or spines are extension of hard endoskeleton

–The water vascular system is unique to echinoderms Network of water-filled canals that branch into tube feet Suction cup–like tube feet used for feeding, gas exchange, and locomotion –Embryonic features such as bilateral symmetry places echinoderms on the same clade as chordates

LE 18-13a Stomach Anus Canals Tube feet Spines

LE 18-13b Tube foot

LE 18-13c Tube foot Spine

18.14 Our own phylum, Chordata, is distinguished by four features –Four distinctive features appear in the embryos, and often in the adults, of chordates, phylum Chordata: A dorsal, hollow nerve cord A stiff notochord Pharyngeal slits A muscular post-anal tail

–The simplest chordates are tunicates and lancelets Marine invertebrates that use pharyngeal slits for suspension feeding Tunicates: small, saclike; adhere to rocks and reefs; likely represent the deepest branch of the chordate lineage Lancelets: small, bladelike; live in marine sands; closest living relatives of the vertebrates

LE Ancestral chordate Head Lungs or lung derivatives Vertebral column Brain Jaws Lobed fins Legs Amniotic egg Milk Mammals Reptiles Amphibians Lobe-fins Ray-finned fishes Sharks, rays Lampreys Hagfishes Lancelets Tunicates Chordates Craniates Vertebrates Jawed vertebrates Tetrapods Amniotes