Invertebrates 1

1. Invertebrates 1 Introduction, Porifera, Cnidaria

2. Lecture outline • Overview: Invertebrate lectures • What is an animal? • Introduction to major phyla in Kingdom Animalia • Basic phylogeny of Kingdom Animalia • Phylum Porifera • Phylum Cnidaria

3. 1. Overview of Invertebrate portion of course • Evolutionary relationships • Body plan • How animal meets its basic needs • Relationship of structure and function • Selected aspects of life-history and ecology

4. 2. What is an animal? • Eukaryotic • Multicellular: Multiple cell types (Not just many cells) • Heterotrophic • No cell wall • Characteristics of early development (unique!) • Blastula and gastrula stages unique to animals • Sponges, have precursors to these stages

5. Phylum Porifera: sponges

6. Phylum Cnidaria: Have Cnidocytes

7. Phylum Ctenophora:The comb jellies

8. Phylum Platyhelminthes:The flatworms

9. Phylum Nematoda:The roundworms

10. Phylum Annelida:The segmented worms

11. Phylum Mollusca:The “soft-bodied” animals

12. Phylum Arthropoda:Jointed appendages

13. Phylum Echinodermata:Spiny-skinned

14. Phylum Chordata:Animals with notochords

15. 4. Phylogenetic overview • Presumed to be monophyletic • Hypothesis assumes all animals evolve from a single common ancestor • That ancestor thought to be a sponge-like protist called a choanoflagellate • Modern choanoflagellate • Found in aquatic habitats • Some propose polyphyletic origins • Cite Cambrian explosion

17. Phylogenetic overview (“traditional”)

18. Multicellularity separates the ancestral protists from all animals • Multicellularity • Different types of cells!

19. Development of two true tissue layers • Separates Phylum Porifera from all others • Sponges All other groups (2-3 tissues)

20. Development of a third germ layer and bilateral symmetry • Cnidarians, Ctenophores All others • Radial symmetry, 2 layers Bilateral symmetry, 3 layers • (Porifera)

21. Further developments (briefly)

22. Body cavities • Acoelomate • Pseudocoelomates • Coelomates

23. Further developments (briefly)

24. 5. Phylum Porifera: The sponges

25. Evolutionary relationships • Simplest multicellular animals • Main cell type, choanocyte, resembles choanoflagellate cell • Considered "multicellular" rather than colonial, because there are different cell types. • Not much, if any cooperation between cells • No real "tissues", no "systems" of any type (no nervous system, circulatory system, etc.)

26. Sponge structure • Review key parts…

27. Water movement and feeding • Role of flagellum • Role of collar • Movement of particles • Phagocytosis

28. Protection • Sponges are sessile… • Toxins/warning coloration (this is why many sponges are brightly colored) • Painful or sharp covering (spicules) • Regenerative ability • Camouflage (if not toxic) • Bore into shells. • NOTE: Nudibranch predators co-opt sponge defenses (toxins, spicules)

29. Phylum Cnidaria

31. Evolutionary relationships • Diverge from the Porifera in the following ways: • Diploblastic: two true tissue layers • Ectoderm and endoderm • No mesoderm • Radiata: One of two phyla to exhibit radial symmetry

32. Where Cnidarians fit in… • Cnidarians, Ctenophores All others • Radial symmetry, 2 layers Bilateral symmetry, 3 layers • (Porifera)

33. Body organization • Polyps and medusae

34. Key features • Polyps and medusae • Tissue layers • Ectoderm, gastroderm (=endoderm) • Mesoglia • Secreted from the tissue layers • Gastrovascular cavity • Functions • Not a true body cavity! • Nervous system: nerve net • No other major body systems • Tentacles with cnidocytes (stinging cells)

35. Nervous system features • True neurons • Conduction can be unidirectional or bidirectional along neurons • Nerve net with no direct pathways • Have simple sensory organs

36. Cnidocytes/nematocystsHow do they work?

37. Life-history strategies