Invertebrate animal information

1. Lesson Overview Invertebrate Evolution and Diversity
Lesson Overview
26.1 Invertebrate Evolution
and Diversity

2. Lesson Overview Invertebrate Evolution and Diversity
THINK ABOUT IT
Many modern multicellular phyla first appeared during a period called
the “Cambrian Explosion,” between 530 and 515 million years ago.
How did so many kinds of animals evolve so quickly? What simpler
forms could they have evolved from?

3. Lesson Overview Invertebrate Evolution and Diversity
Origins of the Invertebrates
When did the first animals evolve?

4. Lesson Overview Invertebrate Evolution and Diversity
Origins of the Invertebrates
When did the first animals evolve?
Fossil evidence indicates that the first animals began evolving long before
the Cambrian Explosion.

5. Lesson Overview Invertebrate Evolution and Diversity
Origins of the Invertebrates
For roughly 3 billion years after the first prokaryotic cells evolved, all
prokaryotes and eukaryotes were single-celled.
Animals evolved from ancestors they shared with organisms called
choanoflagellates, single-celled eukaryotes that sometimes grow in
colonies.
Choanoflagellates share several characteristics with sponges, the
simplest multicellular animals.

6. Lesson Overview Invertebrate Evolution and Diversity
Traces of Early Animals
Our oldest evidence of multicellular life comes from microscopic
fossils that are roughly 600 million years old.
The first animals were tiny and soft-bodied, so few fossilized
bodies exist.
Recent studies have uncovered incredibly well preserved fossils
of eggs and embryos that are 565-million-years-old.

7. Lesson Overview Invertebrate Evolution and Diversity
Traces of Early Animals
Other fossils from this time period have been tentatively identified as
parts of sponges and animals similar to jellyfish.
Paleontologists have also identified what are called “trace fossils,”
tracks and burrows made by animals whose body parts weren’t
fossilized.

8. Lesson Overview Invertebrate Evolution and Diversity
The Ediacaran Fauna
Some important discoveries about invertebrate life before the Cambrian
Period come from fossils in the Ediacara Hills of Australia.
Strange fossils, which date from roughly 565 to about 544 million years
ago, show body plans that are different from those of anything alive
today.
Many of the organisms were flat and lived on the bottom of shallow
seas.
They show little evidence of cell, tissue, or organ specialization, and no
organization into a front and back end.

9. Lesson Overview Invertebrate Evolution and Diversity
The Cambrian Explosion
The Cambrian Period began about 542 million years ago.
Two major Cambrian fossil sites are in Chengjiang, China, and in the
Burgess Shale of Canada.
Cambrian fossils show that over a period of 10–15 million years,
animals evolved complex body plans, including specialized cells,
tissues, and organs.

10. Lesson Overview Invertebrate Evolution and Diversity
The Cambrian Explosion
A number of Cambrian fossils have been identified as ancient members
of modern invertebrate phyla, such as the fossil of arthropod Marrella
shown.

11. Lesson Overview Invertebrate Evolution and Diversity
The Cambrian Explosion
Some early Cambrian fossils represent extinct groups so peculiar that
no one knows what to make of them.

12. Lesson Overview Invertebrate Evolution and Diversity
The Cambrian Explosion
By the end of the Cambrian Period, all the basic body plans of modern
phyla had been established.
Later evolutionary changes, which produced the more familiar body
structures of modern animals, involved variations on these basic body
plans.

13. Lesson Overview Invertebrate Evolution and Diversity
Modern Invertebrate Diversity
Today, invertebrates are the most abundant animals on Earth.
Invertebrates live in nearly every ecosystem, participate in nearly every
food web, and vastly outnumber so-called “higher animals,” such as
reptiles and mammals.

14. Lesson Overview Invertebrate Evolution and Diversity
Cladogram of Invertebrates
What does the cladogram of invertebrates illustrate?

15. Lesson Overview Invertebrate Evolution and Diversity
Cladogram of Invertebrates
What does the cladogram of invertebrates illustrate?
The cladogram of invertebrates presents current hypotheses about
evolutionary relationships among major groups of modern invertebrates. It
also indicates the sequence in which some important features evolved.

16. Lesson Overview Invertebrate Evolution and Diversity
Cladogram of Invertebrates
This cladogram of invertebrates shows current hypotheses of evolutionary
relationships among modern invertebrates. Groups shown close together
are more closely related than are groups shown farther apart. The
sequence in which some important features evolved is also shown.

17. Lesson Overview Invertebrate Evolution and Diversity
Sponges
Phylum: Porifera (“pore bearers”)
Sponges are the most ancient members of the kingdom Animalia.
They are multicellular, heterotrophic, lack cell walls, and contain a few
specialized cells.

18. Lesson Overview Invertebrate Evolution and Diversity
Cnidarians
Phylum: Cnidaria—includes jellyfishes, sea fans, sea anemones,
hydras, and corals
Cnidarians are aquatic, soft-bodied, carnivorous, radially
symmetrical animals with stinging tentacles arranged in circles
around their mouths.
They are the simplest animals to have body symmetry.

19. Lesson Overview Invertebrate Evolution and Diversity
Arthropods
Phylum: Arthropoda (arthron = “joint,” podos = “foot”)—includes
spiders, centipedes, insects, and crustaceans
Arthropods have bodies divided into segments, a tough external
skeleton called an exoskeleton, cephalization, and jointed
appendages, which are structures such as legs and antennae that
extend from the body wall.
Arthropods appeared in the sea about 600 million years ago and have
since colonized freshwater habitats, land, and air.

20. Lesson Overview Invertebrate Evolution and Diversity
Nematodes (Roundworms)
Phylum: Nematoda
Nematodes are unsegmented worms with pseudocoeloms,
specialized tissues and organ systems, and digestive tracts with two
openings—a mouth and an anus.
Nematodes were once thought to be closely related to flatworms,
annelids, and mollusks but have been found to be more closely
related to the arthropods.

21. Lesson Overview Invertebrate Evolution and Diversity
Flatworms
Phylum: Platyhelminthes
Flatworms are soft, unsegmented, flattened worms that have tissues
and internal organ systems.
They are the simplest animals to have three embryonic germ layers,
bilateral symmetry, and cephalization.
Flatworms do not have coeloms.

22. Lesson Overview Invertebrate Evolution and Diversity
Annelids
Phylum: Annelida (annellus = “little ring”)—includes earthworms,
some marine worms, and leeches
Annelids are worms with segmented bodies and a true coelom
lined with tissue derived from mesoderm.

23. Lesson Overview Invertebrate Evolution and Diversity
Mollusks
Phylum: Mollusca—includes snails, slugs, clams, squids, and
octopi
Mollusks are soft-bodied animals that have an internal or external
shell.
They have true coeloms surrounded by mesoderm and complex
organ systems.
Many mollusks have a free-swimming larva, or immature stage,
called a trochophore.

24. Lesson Overview Invertebrate Evolution and Diversity
Echinoderms
Phylum: Echinodermata (echino = “spiny,” dermis = “skin”)—
includes sea stars, sea urchins, and sand dollars
Echinoderms have spiny skin and an internal skeleton.
They also have a water vascular system—a network of water-
filled tubes that include suction-cuplike tube feet, which are used
for walking and gripping prey.
Most exhibit five-part radial symmetry and are deuterostomes.