DECK ABILITY

• Animals live nearly everywhere
• Of the 1,300,000 species in kingdom Animalia


  • Most are invertebrates
  • Only one phylum contains vertebrates, which have a segmented backbone
• What is an animal?

  Multicellular, eukaryotic heterotrophs whose cells secrete extracellular matrix but do not have cell walls. Most digest their food internally.
• Blastula


  A stage in embryonic development that is unique to animals
• Animal life began


  In the water
• The ancestor of animals probably resembled a choanoflagellate
• The oldest animal fossils formed

  About 570 MYA
• These animals lived in water, and existing animal diversity reflects this aquatic heritage
• The Ediacarans were soft, flat organism that lived in the late Precambrian and early Cambrian periods
• Animals diversified greatly during the Cambrian period
• Animal features that reflect shared ancestry

  • Differences in development account for major groupings of animal phyla
  • All animals except sponges have true tissues
  • In most phyla, animal bodies have radial symmetry or bilateral symmetry. Cephalization is correlated with bilateral symmetry
  • An animal zygote divides mitotically to form a blastula and then usually a gastrula. In some animals, the gastrula has two tissue layers (ectoderm and endoderm). In others, a third layer (mesoderm) forms between the other two
  • Bilaterally, symmetrical animals are protostomes if the gastrula's first indentation forms into the mouth. In deuterostomes, the first indentation develops into the anus
• Additional characteristics biologists consider

  • Some types of animals have a body cavity (coelom or pseudocoelom) that can act as a hydrostatic skeleton
  • An animal may have incomplete digestive tract (gastrovascular cavity) or a complete digestive tract
  • Segmentation improves flexibility and increases the potential for specialized body parts
• Sponges


  • Simple animals that lack differentiated tissues
  • Aquatic, sessile animals that are either asymmetrical or radially symmetrical
  • Their porous bodies filter small food particles out of water
  • Although they lack tissues, sponges have specialized cell types, including collar cells and amoebocytes
  • Their skeleton consists of spicules or organic fibers (or both)
• Cnidarians


  • Radially symmetrical, aquatic animals
  • Mostly marine animals that capture prey with tentacles and stinging cnidocytes
  • They digest food in a gastrovascular cavity
  • They move by contracting muscle cells that act on a hydrostatic skeleton
  • Their body form is a sessile polyp or a swimming medusa
  • Examples include corals, hydras, and jellyfishes
• Flatworms


  • Have bilateral symmetry and incomplete digestive tracts
  • Unsegmented animals that lack a coelom
  • The flat body shape allows individual cells to exchange gases with their environment
  • Include free-living flatworms such as planarians, and parasitic flukes and tapeworms
  • Lack circulatory and respiratory systems, but have specialized structures to maintain water balance
  • Have simple nervous systems and hydrostatic skeletons
• Mollusks


  • Soft, unsegmented animals with bilateral symmetry and a complete digestive tract
  • The main groups are chitons, bivalves, gastropods, and cephalopods
  • The mollusk body includes a mantle, a muscular foot, and a visceral mass
  • Most mollusks have a shall, and many have a tonguelike radula
  • They are filter feeders, herbivores, or predators
  • Cephalopods such as octopuses have complex sensory and nervous systems
• Annelids


  • Segmented worms with bodies consisting of repeated segments
  • Include earthworms, leeches, and polychaetes, and they feed in diverse ways
  • Have a complete digestive tract, a closed circulatory system, and respiratory, excretory, and nervous systems
  • The coelom acts as a hydrostatic skeleton
• Nematodes


  • Unsegmented, cylindrical worms that molt periodically
  • Include parasite and free-living species in soil and aquatic sediments
  • Have diverse diets and complete digestive tracts
  • The pseudocoelom aids in circulation and is a hydrostatic skeleton
• Arthropods


  • Segmented animals with jointed appendages and a chitin-rich exoskeleton
  • Like nematodes, arthropods molt periodically
  • Exhibit great diversity in feeding, respiratory systems, excretory systems, nervous systems, and reproduction
  • Life cycles may include metamorphosis
  • Have open circulatory system
• Extinct and extant arthropod groups

  • Trilobites
  • Chelicerates (horseshoe crabs and arachnids)
  • Mandibulate arthropods (centipedes, millipedes, crustaceans, insects)
  • Insects are by far the most diverse arthropods
• Echinoderms


  • Spiny-skinned marine animals
  • Are deuterostomes, as are the chordates
  • Adult echinoderms have radial symmetry; larvae are bilaterally symmetrical
  • The water vascular system enables echinoderms to move, sense their environment, acquire food, exchange gases, and get rid of metabolic wastes
• Characteristics shared by chordates

  • Notochord
  • Dorsal hollow nerve cord
  • Pharyngeal pouches or slits in the pharynx
  • Postanal tail
• Most chordates also have a cranium that protects the brain
• Other features that distinguish chordates

  • Vertebrae
  • Jaws
  • Lungs
  • Presence of limbs in tetrapods
• Amniotic eggs


  Eggs in which the amnion and other membranes protect the developing embryo
• Amniotes


  A clade that includes mammals and reptiles
• Ectotherms


  Lack internal temperature control mechanisms
• Endotherms


  Use heat from metabolism to maintain body temperature
• Tunicates


  • Obtain food and oxygen with a siphon system
  • A tunicate larva has all four chordate characteristics, but adults retain only the pharyngeal slits
• Lancelets


  • Resemble eyeless fishes; adults have all four chordate characteristics
• Hagfishes


  • Have a cranium of cartilage, but they are not vertebrates
  • They secrete slime and lack jaws
• Lampreys


  • Vertebrates that resemble fishes, but they are jawless
• Vertebrate adaptations originating in fishes

  • Vertebral column
  • Jaws
  • Lungs
  • Paired fins that were later modified as limbs
• Cartilaginous fishes


  • Include skates, rays, and sharks
  • Sharks detect vibration from prey a lateral line system
• Bony fishes


  • Account for 96% of existing fish species
  • Have lateral line systems and swim bladders, which enable them to control their buoyancy
  • The two groups are the ray-finned fishes and lobe-finned fishes, which are further subdivided into lungfishes and coelacanths
• Amphibians


  • Breed in water and must keep their skin most to breathe
  • Adaptations to life on land include a sturdy skeleton, lungs, and limbs
  • Include frogs, salamanders and newts, and caecilians
• Reptiles


  • Have efficient excretory, respiratory, and circulatory systems
  • Internal fertilization and amniotic eggs permit reproduction on dry land
  • Nonavian reptiles include lizards and snakes, turtles and tortoises, and crocodilians
• Birds


  • Retain scales and egg-laying from reptilian ancestors
  • Honeycombed bones, streamlined bodies, and feathers are adaptation that enable flight
  • Unlike the other reptiles, birds are endothermic
• Mammals


  • Have fur, secrete milk from mammary glands, and have distinctive teeth and highly developed brains
  • Monotremes are mammals that hatch amniotic egg
  • The young of marsupial mammals are born after a short pregnancy and often develop inside the mother's pouch
  • Placental mammals have longer pregnancies; the young are nourished by the placenta in the mother's uterus
• Fossils and DNA tell the human evolution story