Chapter 9

1. Chapter 9 Multicellular and Tissue Levels of Organization

2. Evolutionary Perspective • Porifera • No tissues • Division of labor among independent cells • Independent origin from common animal ancestor • Choanoflagellate protists (?) • Cnidaria and Ctenophora • Tissue level organization • Independent origins from common animal ancestor • Choanoflagellate protists (?) • Origins of Multicellularity • At least 800 million years—Precambrian • Colonial hypothesis • Syncytial hypothesis

3. Figure 9.1 Evolutionary relationships of the Porifera, Cnidaria, and Ctenophora.

4. Figure 9.2 Two hypotheses regarding the origin of multicellularity. (a) Colonial hypothesis. (b) Syncytial hypothesis.

5. Phylum Porifera • Asymmetrical or superficially radially symmetrical • Three cell types: pinacocytes, mesenchyme cells, and choanocytes • Central cavity, or a series of branching chambers, through which water circulates during filter feeding • No tissues or organs

6. Table 9.1

7. Cell Types, Body Wall, and Skeletons • Pinacocytes • Outer surface • Some contractile, others may be specialized into porocytes • Mesohyl • Jellylike middle layer • Mesenchyme cells • Amoeboid cells • Reproduction, secreting skeletal elements, transporting and storing food, form contractile rings • Choanocytes • Flagellated • Collarlike ring of microvilli • Water currents for filter feeding • Skeleton • Spicules • Spongin

8. Figure 9.4 Morphology of a simple sponge.

9. Figure 9.5 Sponge spicules.

10. Figure 9.6 Water Currents and Body Forms. • Complex sponges have increased surface area for filtering large volumes of water.

11. Maintenance functions • Filter feeding • Bacteria, algae, protists, suspended organic matter • Trapped in choanocyte collar and incorporated into food vacuole • Digestion by lysosomal enzymes and pH changes • Nitrogeneous waste removal and gas exchange • Diffusion • Coordination • Responses of individual cells (some coordination)

12. Reproduction • Monoecious • Choanocytes (and sometimes ameboid cells) lose collars and flagella and undergo meiosis. • External fertilization and planktonic larvae in most • Asexual reproduction • Gemmules • Freshwater and some marine

13. Figure 9.7 Development of sponge larval stages. Parenchymula larva. (b) Amphiblastula larva. (c) Gemmule. (d)

14. Phylum Cnidaria • Radial symmetry or modified as biradial symmetry • Diploblastic, tissue-level organization • Gelatinous mesoglea between the epidermal and gastrodermal tissue layers • Gastrovascular cavity • Nerve cells organized into nerve net • Specialized cells, called cnidocytes, used in defense, feeding, and attachment

15. The Body Wall • Epidermis • Outer cellular layer • Ectodermal origin • Gastrodermis • Inner cellular layer • Endodermal origin • Mesoglea • Jellylike • Cells present but origins are epidermal or endodermal

16. Figure 9.8 Body wall of a cnidarian.

17. Nematocysts • Cnidocytes • Epidermal or gastrodermal cells that produce cnida • 30 types • Nematocysts used in food gathering and defense

18. Figure 9.9 Cnidocyte structure and nematocyst discharge.

19. Figure 9.10 The generalized cnidarian life cycle involves alternation between a sexual medusa stage and an asexual polyp stage.

20. Maintenance Functions • Gastrovascular cavity • Digestion • Gas exchange • Excretion • Reproduction • Hydrostatic skeleton • Support and movement • Epitheliomuscular cells act against water-filled cavity. • Nerve net coordinates body movements.

21. Reproduction • Medusa • Dioecious • External fertilization most common • Planula larva • Polyp • Budding produces miniature medusae.

22. Class Hydrozoa • Mostly marine • Some freshwater • Unique features • Nematocysts only epidermal • Gametes epidermal and released to outside of body • Mesoglea largely acellular • Medusae with velum

23. Figure 9.11 Obelia structure and life cycle.

24. Figure 9.12 Gonionemus medusa. The velum is unique to members of the Hydrozoa.

25. Class Staurozoa Figure 9.13 Members of the class Staurozoa are marine and lack a medusa stage. Lucernaria janetae is shown here.

26. Class Scyphozoa • Marine • Medusa dominant in life history • Lacks velum • Cnidocytes epidermal and gastrodermal • Gametes gastrodermal • Dioecious

27. Figure 9.14 Representative scyphozoans (a) Mastigias qinquecirrha and (b) Aurelia labiata. (b) (a)

28. Figure 9.15 Structure of the scyphozoan medusa of Aurelia.

29. Figure 9.16 Aurelia life history.

30. Class Cubozoa • Cuboidal medusa • Tentacles hang from corners • Tropical • Dangerous nematocysts Figure 9.17 The sea wasp, Chironex fleckeri.

31. Class Anthozoa • Colonial or solitary • Lack medusa • Cnidocytes lack cnidocils • Anemones and corals • Mouth leads to pharynx • Mesenteries divide gastrovascular cavity and are armed with nematocysts. • Mesoglea with ameboid mesenchyme cells

32. Figure 9.18 (a) The giant sea anemone (Anthopleura xanthogrammica) and (b) a sea anemone (Callictis parasitical) living in a mutualistic relationship with a hermit crab.

33. Figure 9.19 The structure of the anemone, Metridium sp.

34. Reproduction • Asexual • Pedal laceration • Longitudinal or transverse fission • Sexual • Monoecious or dioecious • External fertilization produces planula. • Monoecious species • Protandry • Male gametes mature first.

35. Corals • Stony • Reef forming • Lack siphonoglyphs • Cuplike calcium carbonate exoskeleton • Asexual budding expands colony. • Symbiotic relationship with zooxanthellae

36. Figure 9.20 A stony coral polyp in its calcium carbonate skeleton.

37. Corals • Octacorallian • Warm waters • Eight pinnate tentacles • Eight mesenteries • Internal protein or calcium carbonate skeleton

38. Figure 9.21 Octacorallian corals (a) Ptilosaurus gurneyi and (b) Gorgonia ventalina.

39. Phylum Ctenophora • Diploblastic or possibly triploblasitic • Biradial symmetry • Gelatinous, cellular mesoglea • True muscle cells • Gastrovascular cavity • Nerve net • Colloblasts • Eight comb rows

40. Table 9.3

41. Phylum Ctenophora • Cellular mesoglea and true muscle cells suggest that members may be triploblastic. • Locomotion by bands of cilia are called comb rows. • Tentacles contain adhesive cells called colloblasts that capture prey. • Monoecious with gastrodermal gonads • External fertilization leads to flattened larval stage.

42. Figure 9.22 (a) The bioluminescent ctenophoran Mnemiopsis sp. (b) The structure of Pleurobranchia. (c) Colloblast structure. (a)

43. Further Phylogenetic Considerations • Porifera • Oldest fossil deposits • Choanoflagellate ancestors • Increases surface-to-volume ratio in syconoid and leuconoid body forms evolved in response to selection for increased size. • Cnidaria • Radially symmetrical ancestor • Minority view suggest bilateral ancestor. • Molecular data and morphology suggests relationships shown in figure 9.23. • Ctenophora • Relationships to other groups uncertain but probably distant

44. Figure 9.23 Cladogram showing cnidarian taxonomy.