The Metazoa (Differentiated Multicellular Animals) An Overview of the Major Groups

1. The Metazoa (Differentiated Multicellular Animals) An Overview of the Major Groups

2. How Do We Classify Life ? Note: Kingdoms Eubacteria and Archaea formerly classified as Kingdom Monera

3. Three Domains Archaea Eukarya Bacteria

4. Now Three Domains and 6 Kingdoms

5. Conventional Classification of Major Phyla Protista amoebas, foraminifera, radiolaria (presumed ancestors of Metazoa) Metazoa Porifera sponges Cnidaria/Coelenterata sea anemones, corals, sea pens, etc. Several “worm” phyla flatworms, annelids, etc. Brachiopoda brachiopods (“lamp shells”) Bryozoa bryozoans (“moss animals”) Mollusca snails, clams, cephalopods, etc. Arthropoda shrimps, crabs, insects, spiders, etc. Echinodermata starfish, sea urchins, crinoids, etc. Hemichordata acorn worms, graptolites, etc. Chordata lancelet, vertebrates, etc.

6. Discovery of classic “Ediacaran Fauna” (about 543 Ma) Pound Quartzite Ediacara Hills, north of Sydney, Australia Metazoan Fossils Found in 1946 Classification: lumped together as “medusoids”

7. Details originally overlooked: A diverse assemblages of fossils Mawsonites Spriggina Dickinsonia

8. Mistaken Point, Newfoundland 565 Ma “spindles”

9. Portugal Cove Newfoundland Up to about 575 Ma Charniodiscus (fronds)

10. Latest Proterozoic (Ediacaran Period) Oxygenated atmosphere and seas Complex, soft-bodied metazoa

11. Were Vendian organisms Early representatives of modern phyla ? Sea Pen Nudibranch Ostrich plume hydroid

12. Adolph Seilacher Concept of “Vendozoa: (Extinct phylum ? Probably not.) soft bodied “quilted” structure (fluid-filled bags ?” Dependent on microbial mats “mat stickers”: fixed to seafloor, photosynthesizers “mat scratchers”: grazed on microbial mats No carnivores !

13. How do You Make a Metazoan ? You Have to Start Out Simple. Single celled Protista Amoebas, Foraminifera, Radiolaria, etc.

14. Phylum Protista: the importance of choanoflagellates A choanoflagellate is a protist with a collared cell and a flagellum

15. Some choanoflagellates form colonies In such colonies, all individuals cooperate in moving their flagella, generating a current from which food particles can be extracted

16. On to the Metazoa…

17. Phylum Porifera (Sponges) Most Basic Metazoan Plan of Cowen Single layer of tissue (collared cells) Sponges also have collared cells, but these form a larger, integrated structure supported by rigid spicules or organic tissue. The differentiation of cells required the evolution of Hox Genes (genes that dictate differing functions of cells)

18. Similar to some of the Ediacaran animals (remember the frond-like creatures), sponges show a fractal organization Leucon-grade sponge (contains multiple “sycon” elements) Sycon-grade sponge (contains multiple “ascon” elements) Ascon-grade sponge

19. Phylum Cnidaria / Coelenterata (Second Metazoan Body Plan of Cowen) 2 layers of tissue: ectoderm, endoderm (probably resulted from invagination of ectoderm)

20. Phylum Cnidaria / Coelenterata Hydra hard corals sea pens sea anemones soft corals jellyfish 2 tissue layers: ectoderm, endoderm

21. Computer-generated fractal Natural coral Again, in the more complex forms of these simple organisms fractal geometry is apparent

22. “Worms” or “Bilaterans” Most Complex Metazoan Body Plan of Cowen triploblastic - 3 principal cell layers ectoderm, mesoderm, endoderm Basic bilateral symmetry: fractal geometry breaks down, but tissue differentiation is incredible !

23. The Coelom The Ectoderm and Endoderm can be viewed as essentially solid, continuous layers. The Mesoderm is a little more complicated in that it actually lines a fluid-filled body cavity called the coelom. It is within the coelom that internal organs other than the gut develop (e.g. respiratory organs)

24. Coelom and Orifice Development; Protostomes In the Protostomes (including molluscs, annelid worms and arthropods), the coelom develops directly from mesodermal tissue. Another distinguishing characteristic to the protostomes is the development of the mouth before the anus in the young embryo

25. Coelom and Orifice Development; Deuterostomes In the Deuterostomes (including echinoderms and chordates), the coelom develops from outpockets of the gut (endoderm) Another distinguishing characteristic to the protostomes is the development of the anus before the mouth in the young embryo (blastophore)

26. The Evolution of the Coelom The coelom may have initially evolved as a hydraulic device. A bilateran with a coelom can squeeze its internal fluids with body muscles. This squeezing bulges the body wall at the weakest point, and can be used as a “power drill” for burrowing (think about how a worm gets around).

27. The Evolution of the Coelom In addition, this pumping could facilitate the transport of oxygen through the body without relying on the bathing of tissues in oxygenated water by diffusion through a thin ectoderm. This means that animals could efficiently deliver oxygen throughout their bodies without compromising the effectiveness of their outer skins (ectoderm) or size. This also meant that animals could evolve exoskeletons.

28. The Protostomes can be subdivided in two smaller groups • (clades): • Lophotrochozoa • Ecdysozoa

29. Lophotrochozoa: This group gets its confusing name from two related subgroups (linked by molecular phylogenetic studies): 1. The trochozoa - animals with distinctive, fuzzy, trochophore larvae, which include the phyla Platyhelminthes and the Mollusca. 2. The lophophora – animals which feed via a fringe of hollow tentacles, called a lophophore), which include the phyla Brachiopoda and Bryozoa. trochophore larva Lophophore (in brachiopod)

30. Important Lophotrochozoans

31. Lophotrochozoa: Phylum Platyhelminthes (flatworms) Flatworms do not have a coelom, and it is likely that something like a flatworm gave rise to more advanced coelomate bilaterans.

32. Lophotrochozoa: Phylum Mollusca Each class derived from HAM (hypothetical ancestral mollusc) Key Features: gut mantle cavity radula (rasping organ) gills foot

33. Lophotrochozoa: Phylum Mollusca Gastropods Bivalves Cephalopods (squids, octopuses, cuttlefish, ammonoids)

34. Lophotrochozoa: Phylum Brachiopoda (“arm foot”) Key Features: pedicle, gut, muscles, lophophore

35. Lophotrochozoa: Phylum Bryozoa (“moss animals”) Key Features: colonial habit, lophophore

36. Ecdysozoa: This group includes animals that moult their outer covering as they grow. Phylum Arthropoda is the primary phylum of this group.

37. Important Ecdysozoa

38. Ecdysozoa: Phylum Arthropoda Insects Spiders Crabs Lobsters Barnacles Etc. trilobites eurypterids Key Features: Jointed appendages 3-fold division of body (head, thorax, abdomen) scorpions shrimps

39. Important Deuterostomes (Deuterostomia)

40. Deuterostomia: Phylum Echinodermata (“spiny skin”) Sea urchins Brittlestars Crinoids Starfish Sea cucumbers Key Features: 5-fold symmetry, calcite plates (but embryos are bilateral, suggesting a bilateral ancestor)

41. Deuterostomia: Phylum Hemichordata Key Characteristics: 3-part division of body (preoral lobe, collar, trunk) Pharynx Gill slits Stomochord Pterobranchs Graptolites Acorn worms

42. Deuterostomia: Phylum Chordata Key Features: notochord dorsal nerve cord, pharynx gills slits post-anal tail Sea squirts and salps (Urochordates) Amphioxus (lancelet) (Cephalochordates)

43. END OF LECTURE