Bio1151 Chapter 32 An Introduction to Animal Diversity
  1. Animals are multicellular,                eukaryotes that ingest their food.

    All of these diverse organisms are animals.
  2. The ancestor of animals diverged from those of        about 1.2 billion-800 million years ago, and may have resembled modern                    .

    The closest living relatives to Animalia are the colonial protist choanoflagellates. These cells possess a collar (choanos in Greek) around a flagellum. They resemble the specialized choanocytes of multicellular sponges.
  3. The kingdom diversified about 525 million years ago, during the           explosion, when many animal phyla appeared.

    A diverse array of animals was found in fossils from the Burgess Shale site in British Columbia, dating from the Cambrian period.

    They include:

    Pikaia (swimming eel-like chordate)

    Hallucigenia (with spikes on seafloor)

    Anomalocaris (large clawed predator)

    Marella (arthropod swimming at left)

    Ottoia (burrowing U-shaped worm) Cambrian exhibit at Field Museum.

  4. Animals can be categorized by how their cells are organized according to a       plan.

    Kingdom Animalia can be classified by morphological traits that define body plans:

  5. being multicellular (Metazoa)
  6. possessing tissues (Eumetazoa)
  7. bilateral symmetry (Bilateria)
  8. embryonic development (Deuterostomia)
    •         symmetry is like a flower pot, the body radiates from the center.

      Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.
    •            symmetry has a single plane of symmetry.

      Animals with bilateral symmetry have a single plane of symmetry that divides the body into right and left sides, as well as a dorsal (top) side and a ventral (bottom) side. This also allows for cephalization, the development of a head, where a nervous system and specialized sensory organs can be stored.
    • Most animals have          that develop from embryonic layers of the           .

      Embryonic tissue development in animals. Cleavage of the zygote by successive mitotic divisions produces a blastula, a hollow ball of cells. Then the embryo folds in at the blastopore toward the blastocoel (cavity), forming a gastrula with germ layers of embryonic tissues: the ectoderm and the endoderm; some animals have an additional layer, mesoderm. Germ layer development
    • Diploblastic animals such as jellyfish have      germ layers:           and           .

      Diploblastic animals have two germ layers: an outer ectoderm and an inner endoderm.

      The jellyfish has a single opening for a mouth and an anus.

    • Triploblastic animals have        germ layers, including a           .

      Triploblastic animals such as humans have three germ layers. An outer ectoderm surrounds a mesoderm. The inner endoderm folds inward at the blastopore, forming the archenteron (embryonic digestive tube).
    • The mesoderm may develop into tissue that line a fluid-filled space called a         .

      Coelomates such as earthworms have a true coelom, a body cavity completely lined by tissue derived from mesoderm and surrounding a digestive tract derived from endoderm.

      The coelom separates and suspends the organs from the body, providing cushioned support and room to grow, as well as separate openings for the mouth and anus.

      • A               is a body cavity only partially lined by mesoderm tissues.

        Pseudocoelomates such as nematodes have a body cavity partially lined by tissue derived from mesoderm. Note the digestive tract is not covered by mesoderm tissue.
      • Organisms without a body cavity are considered              .

    Acoelomates such as Planarians lack a body cavity between the digestive tract and body wall.
  9. The coelomates show two major modes of development.
    • Protostomes develop their        from the blastopore of the gastrula.

      Protostomes such as molluscs and annelids exhibit spiral cleavage. Protostomes form their coelom by splitting of the mesoderm. Protostomes develop their mouth from the blastopore of the gastrula. The anus is formed from a second opening.
    • Deuterostomes develop their       from the blastopore.

    Deuterostomes such as echinoderms and chordates exhibit radial cleavage. Deuterostomes form their coelom by infolding of the archenteron. Deuterostomes develop their anus from the blastopore of the gastrula. The mouth is formed from a second opening.
  10. Current phylogeny places            as a clade with true          , and divides the Bilateria into three clades:                , Lophotrochozoa, and Ecdysozoa.

    Lophotrochozoa (Mollusca, Annelida) are distinguished by a ciliated feeding structure (lophophore) or a trochophore larva.

    Ecdysozoa (Arthropoda, Nematoda) have exoskeletons that are shed in a process called ecdysis (molting).

    This cicada is in the process of emerging from its old exoskeleton.

    The animal then secretes a new, larger exoskeleton.

    Review and exercise: