Chapter 33

Invertebrates

Invertebrates• Lack a backbone• Account for 95% of all known

animal species.• All but one of the 35 animal

phyla.

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.

Bilateral Symmetry• Most animals

are bilaterally symmetrical, and have triploblastic development.

• Platyhelminthes flatworms

Rotifera• Tiny animals

inhabiting fresh water, marine, and damp soil.

• Unique because many of them reproduce via parthenogenesis.

Parthogenesis• Females produce offspring

from unfertilized eggs.

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.

Parthogenesis• Some rotifers produce

females.• These females lay more

unfertilized eggs that develop into more females.

Mollusca• Have a muscular

foot.• A visceral mass

containing internal organs.

• A mantle, a tissue that secretes a shell.

Annelida• Segmented worms.

Arthropoda• 2/3’s of all

known species.• They have a

hard exoskeleton and jointed appendages.

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.