Invertebrates

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Chapter 33

• Invertebrates

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Invertebrates

• Lack a backbone
• Account for 95 of all known animal species.
• All but one of the 35 animal phyla.

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Porifera

• Sponges are sedentary suspension feeders.
• They pass water through their pores and extract
  food.
• They are sessile.

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Radial Symmetry

• Cnidarians are invertebrates such as jellyfish,
  corals, and hydras.
• Many inverts have radial symmetry.

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Bilateral Symmetry

• Most animals are bilaterally symmetrical, and
  have triploblastic development.
• Platyhelminthes flatworms

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Rotifera

• Tiny animals inhabiting fresh water, marine, and
  damp soil.
• Unique because many of them reproduce via
  parthenogenesis.

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Parthogenesis

• Females produce offspring from unfertilized eggs.

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Parthogenesis

• Some species of rotifers produce two types of
  eggs.
• One develops into a female, the other into a
  short-lived male.
• The male survives long enough to produce sperm
  that fertilize the eggs.

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Parthogenesis

• Some rotifers produce females.
• These females lay more unfertilized eggs that
  develop into more females.

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Mollusca

• Have a muscular foot.
• A visceral mass containing internal organs.
• A mantle, a tissue that secretes a shell.

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Annelida

• Segmented worms.

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Arthropoda

• 2/3s of all known species.
• They have a hard exoskeleton and jointed
  appendages.

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Echinoderms and Chordata

• Echinoderms are spiny skinned animals such as sea
  stars and sea urchins.
• Chordata are the subphyla of invertebrates that
  contain a notochord but no vertebra.

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