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Animals (ch 23-26) What is an animal? Eukaryotic Multicellular Heterotrophic Lack cell walls Symmetry Asymmetry: No mirror images Radial Symmetry: Mirror images through a central axis Bilateral symmetry: Mirror right and left images when cut down the center of the body Sponges - Phylum Porifera Porifera: The sponges Thought to come from chaonoflagellate colonies Asymmetry and radial symmetry Filter feeders Cnidarians Hydras & Jellyfish 2 life stages: Medusa & Polyp Stinging cells called cnidocytes Phylum Cnidaria Only animals that produce nematocysts Nerve net Hydrostatic skeleton Saclike gut Nematoda Nonsegmented Pseudocoelomate Cylindrical body No circulatory system Complete digestive tract Some free living others parasitic Platyhelminthes Flatworms Simplest bilateral animals Have a distinct head region (cephilization) Incomplete digestive tract (Blind gut) Planarians Free-living flatworms Nonparasitic Eyespots Nerve cords Live on underside of rocks in fresh water Can regenerate body parts Parasitic Flatworms Flukes: Most live in the intestines of the host animal Blood fluke larva infects snails mature fluke in blood vessels of humans Tapeworms: Most live in the digestive tract of host animal Use suckers & hooks to attach Feed by absorbtion Body Plan Acoelomate Pseudocoelomate Coelomate Mollusca Most have a soft body protected by hard shell Gastropods: Snails Bivalves: Clams Cephalopods: Squid and octopus Annelida Segmented worms: Class Polychaeta Marine worms Class Oligochaeta Earthworms Class Hirudinea Leeches Arthropoda Arthropoda means jointed foot Most successful phylum Includes: crayfish, lobsters, crabs, barnacles, spiders, ticks, and insects Exoskeleton First animal to invade land Probably evolved form annelida Insects Number of insect species greater than total of all other species combined On land for over 400 million years Metamorphosis some social (Hymenoptera) Echinodermata Spiny skin” Sea stars & sea urchins water vascular system with tube feet Cleavage Protostomes: Spiral and determinate Deuterostomes: Radial and indeterminate Chordata Dorsal, hollow nerve cord Notochord Gill slits Post-anal tail Tunicates & Lancelets First chordates Tunicates adults are stationary Lancelets are small marine suspension feeders Vertebrata Backbone composed of vertebrae Skull Skeletal system Includes: Agnathans, fish, amphibians, reptiles, birds, mammals (including stupid humans) Fishes Agnatha: Jaw-less fish (Lamprey eels) Chondrichthyes: Chartilaginous fish (sharks and rays) Osteichthyes: bony fish Includes lobe-finned fish (Coelacanth) Jawed Fishes Most diverse and numerous group of vertebrates Two classes: Chondrichthyes (cartilaginous fishes) Osteichthyes (bony fishes) Bony fishes Have a skeleton reinforced by hard calcium salts Have a lateral line system, a keen sense of smell, and excellent eyesight Lobe-Finned Fishes Coelocanths Lunglike sacs do not function in gas exchange Lungfishes Have gills and one lung or a pair Must surface to gulp air Amphibia Amphibios = “Living double life” Must lay eggs in water Must keep skin wet Believed to have evolved from lobe-finned fish Early Amphibians Fishlike skull and tail Four limbs with digits Short neck Reptilia Drought-resistant amniotic egg Scales that retain water Modern reptiles are ectothermic Some dinosaurs may have been endothermic Aves Birds are believed to have evolved from dinosaurs about 150-200 MYA Some bones are hollow and filled with air to reduce weight High metabolic rate Endotherms Adapted for Flight Four-chambered heart Highly efficient respiratory system Lightweight bones with air spaces Powerful muscles attach to the keel Mammalia Believed to have evolved from reptiles ~ 225 MYA Monotremes: Egg-laying (platypus) Marsupials: Pouched mammals (Opossum) Placentals: Embryos inside the mother in the placenta Earliest Primates Primates evolved more than 60 million years ago during the Paleocene First primates resembled tree shrews Long snouts Poor daytime vision From Primates to Humans “Uniquely” human traits evolved through modification of traits that evolved earlier, in ancestral forms Hominoids Apes, humans, and extinct species of their lineages In biochemistry and body form, humans are closer to apes than to monkeys Hominids Subgroup that includes humans and extinct humanlike species
