Overview of Animal Phyla

Introduction to Biology and Animals

• Biology often assumed to focus on animals, but involves much more (cells, genetics, evolution, etc.).
• Fascination with animals persists from childhood.
• Understanding broader biology enhances the understanding of animals.

What is an Animal?

• Multicellular, eukaryotic organisms with specialized cells.
• Heterotrophs (consume food rather than produce it).
• Usually motile at some stage of life.
• Important vocab: symmetry, cephalization, protostomes, deuterostomes, triploblastic.

Key Vocabulary

• Symmetry:
  • Radial symmetry: multiple planes of symmetry (e.g., sessile animals).
  • Bilateral symmetry: single plane of symmetry (e.g., humans).
• Cephalization: Concentration of nerve tissue in the head.
• Protostomes vs. Deuterostomes:
  • Protostomes: First embryonic opening (blastopore) becomes mouth.
  • Deuterostomes: First embryonic opening becomes anus.
• Triploblastic Animals:
  • Have three germ layers: ectoderm, mesoderm, endoderm.
  • Not all are protostomes or deuterostomes.
• Coelom: Body cavity derived from mesoderm.

Nine Major Animal Phyla

1. Phylum Porifera (Sponges)

• Aquatic, mostly sessile, porous body.
• Intracellular digestion, no gut, organs, or true tissue.
• No symmetry, cephalization, or coelom.

2. Phylum Cnidaria (Jellies, Sea Anemones, Hydras)

• Aquatic, one gut opening, radial symmetry.
• Specialized cells for digestion and stinging.

3. Phylum Platyhelminthes (Flatworms)

• Aquatic/terrestrial, one gut opening, bilateral symmetry.
• Cephalization present but no coelom.
• Protostomes.

4. Phylum Nematoda (Nematodes)

• Ecologically impactful, bilateral symmetry, cephalization.
• Pseudocoelom, protostomes, two gut openings.

5. Phylum Mollusca (Mollusks)

• Aquatic/terrestrial, bilateral symmetry, cephalization, coelom.
• Protostomes, diverse from micromollusks to giant squid.

6. Phylum Annelida (Segmented Worms)

• Aquatic/terrestrial, segmented bodies.
• Bilateral symmetry, cephalization, coelom, protostomes.

7. Phylum Arthropoda (Insects, Spiders, Crustaceans)

• Aquatic/terrestrial, jointed appendages, segmented bodies.
• Bilateral symmetry, cephalization, coelom, protostomes.

8. Phylum Echinodermata (Sea Stars, Sea Urchins)

• Aquatic, radial symmetry in adults, regeneration abilities.
• No cephalization, have a coelom, deuterostomes.

9. Phylum Chordata (Vertebrates and Few Invertebrates)

• Aquatic/terrestrial, defined by notochord.
• Bilateral symmetry, cephalization, coelom, deuterostomes.

Conclusion

• The overview covers major characteristics and exceptions.
• Importance of exploring beyond typical images of animals.
• Encouraged continued exploration and curiosity.