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Chapter 30: Intro to Animals

Cookie monster sea sponge

What defines an animal?

  • Multicellular eukaryotes lacking cell walls but with an extensive extracellular matrix

  • Heterotrophs

  • Move under their own power at some point in their life cycle

  • Have neurons and muscle cells (except sponges)

  • Most animals, neurons connect to each other and some neurons connect to muscle cells

  • Animals are the only multicellular heterotrophs that ingest their food first before they digest it

Sponges

  • Most basal lineage of living animals

  • Sponges and choanoflagellates are both sessile filter feeders.

30-35 phyla of animals

  • Animals are a monophyletic group

Important Traits of Animals

  1. The origin of tissues (specialized groups of cells)

    Choanoflagelllates - no tissues, just colonies of identical cells

    Sponges - some have epithelium (surface tissues)

    Diploblasts (comb jellies, jellyfish, sea anenome, coral) - tissues from 2 embryonic germ layers (ectoderm, endoderm)

    Triploblasts (every other animal) tissues from 3 embryonic germ layers

  2. The origin of bilateral symmetry and cephalization/the nervous system

    Did not evolve all at once during the Cambrian explosion. Some corals and anemones (around before the Cambrian) are bilaterally symmetrical.

    Bilateral animals have a nervous system along an axis (like a spinal column)

    Bilateral animals have concentrated nerves and receptors at the most important places rather than evenly dispersed like in radial animals

  3. The origin of the body cavity (coelom)

    Triploblasts have a fluid filled sac called the coelom that allows us to specialize, makes us squishy, gives us room to grow

    Triploblasts have a tube-within-a-tube body plan

    Ectoderm on the outside (skin), endoderm on the inside (guts), mesoderm in between (organs)

    Three types of coelom body plans:

    Coelomates have an enclosed coelom completely lined with mesodermal tissue

    Acoelomates have no enclosed coelom. All they got is guts. Ex. flatworm

    Pseudocoelomates have an eclosed coelom that’s only partially lined with mesodermal tissue

  4. Embryonic origin of the anus

    Protostomes: embryonic development of the mouth before the anus

    So many protostomes, so some of them don’t follow this rule

    Deuterostomes: embryonic development of the anus before the mouth