This document describes key characteristics of different animal phyla. It notes that animals are eukaryotic, multicellular organisms that lack cell walls and obtain nourishment through ingestion. It distinguishes between radial and bilateral symmetry. It discusses the evolution of body cavities which enabled supporting organ systems and material distribution. Germ layers including ectoderm, mesoderm and endoderm are described. Key characteristics of different phyla are outlined such as Cnidarians having stinging cells, Platyhelminthes including many parasitic flatworms, and Chordates possessing a notochord, nerve cord, pharyngeal slits and post-anal tail during embryonic development.

3. Eukaryotic (Domain Eukaryota)
Multi-cellular (unlike most Protists)
Lack cell walls (unlike Plants and Fungi)
Heterotrophic, by ingestion – Animals
obtain their nourishment by ingesting
other organisms (unlike Fungi)

4. Most animals are mobile
Sexual reproduction; haploid cells fuse
directly to produce zygote, and no
alternation of generations
Tissues – cells are organized into
structurally functional tissues

5. Radial symmetry – body
parts arranged around a
central axis (simple)
Bilateral symmetry –
body has a right and a
left half that are mirror
images of each other
(advanced)

6. Evolution of a body cavity enabled the
evolution of supporting organ systems and
a means for distributing materials
The body cavity – a space surrounded by
mesodermal tissue formed during
development
Three germ layers: Ectoderm (outside),
Mesoderm (middle), and Endoderm (inside)

10. The simplest of animals
No nervous, digestive, or circulatory
systems
Sessile
Lack germ layers
No defined
symmetry

11. Nematocysts – stinging cells
Radial symmetry
“Jellyfish”, Corals, Sea anemones
2 Body forms – Polyp & Medusa

12. Colloblasts – sticky cells
Strictly marine
Largely bioluminescent
Sexes are not separate.
Reproduction is sexual

13. No body cavity
Half of all flatworms are parasitic
(flukes, tapeworms, etc)
Sexes are not separate
Fertilization is internal.

14. Pseudocoelomates
Can be free-living or parasitic
Bilaterally symmetrical
Pseudocoelomate
Triploblastic

15. Coelomates
Oligochaetes (earthworms) and
Polychaetes (bristle worms)

16. Mantle – secretes shell; forms siphon and
external flaps
Bivalves (clams, mussels, etc), Snails,
Squid, Octopus, Sea Slugs

17. “Jointed foot”; jointed limbs
rigid cuticle/exoskeleton
Bilaterally symmetrical
Triploblastic
Insects, Arachnids, Crustaceans etc.

18. Strictly marine
Deuterostomes
“Spiny skin”
Includes sea stars, sea urchins, brittle
stars

19. Includes all vertebrates (Subphylum Vertebrata)
All have (at one stage of their life cycle)
– A notochord – a flexible rod; “backbone”
– A hollow, dorsal nerve cord; develops into spinal
cord and brain
– Pharyngeal slits* – filtering apparatus for feeding
– An endostyle* – longitudinal ciliated groove in
pharynx, produces mucus to capture food particles
– A post-anal tail*
*only present during embryonic stage in advanced
vertebrates

20. All Chordates have all four of
these characteristics at some time
in their lives