1 / 40

What is a Metazoan? In other words what are the inherent

Delve into the fundamental characteristics of Metazoans through the unique traits of Placozoa and Cnidaria, showcasing their evolutionary success and diverse adaptations.

grieco
Download Presentation

What is a Metazoan? In other words what are the inherent

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What is a Metazoan? In other words what are the inherent Characteristics of the animal body plan that are different from that of a colonial heterotrophic protists? What are some characteristics of sponges that help us place them directly in the metazoan

  2. Phylum Placozoa -- 2-3 mm, 25 um- thick, resembling a large ameba -- Lacks anterior posterior polarity -- Asexual reproduction is prevalent --The most primitive animal? Trichoplax adhaerens

  3. Phylum Placozoa Dorsal cilium epithelium-like layer Fiber synctium thick glandular layer Flagellated cells Intercellular junctions • - Feed ventrally by absorption of digested material • - Lack organs but tissue-like outer walls • - A bit more than 2000 cells • - Only 4 different cell types • (20 in sponges; > 220 in mammals) • - Smallest genome of all animals

  4. Three competing Scenarios Functional Morph. Epitheliozoa Eumetazoa Earliest view of them as the basal metazoan Special cellular junctions consisting of two opposing dense plaques (desmosomes) not found in most sponges 16S rRNA data…maybe secondarily simplified from more complex ancestors?

  5. Mitochondrial genome of Trichoplax adhaerens supports Placozoa as the basal lower metazoan phylum Dellaporta, Stephen L. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 8751-8756 Largest known mt genome 46 kbp, 2x that of most metazoa with introns and other intrageneic spacers and large protein coding regions that are usually lacking in other animals Blue: known mt proteins Gray: ribosomal genes Green: unknown open reading frames Red lines: introns

  6. (a sponge) Conclusions?

  7. Phylum Cnidaria More than 9, 000 species, including jellyfish, corals, anemones, hydroids and much much more.

  8. Themes • General characteristics of Cnidaria • Why are they successful? • Cnidaria Diversity and Taxonomy • Classes, SubClasses of Anthozoans • Similarity of Polyp and Medusa • The Cnidaria Body Plan • Class Scyphozoa, the jellyfish • Complexity, Sensory & Nervous System

  9. What Characteristics Account for the Great Success of Cnidarians? 1. Two distinct adult forms 2. Diphasic life cycle in some species 3. Ability to proliferate by cloning 4. And to form polymorphic colonies 5. Formidable prey capture device 6. Low Energy Demands

  10. What Characteristics Account for the Great Success of Cnidarians? 1. Two Very Different Adult Forms Polyp Medusa

  11. What Characteristics Account for the Great Success of Cnidarians? 2. Dimorphic Life Cycle in Many Species Life cycle Of the Hydroid Obelia

  12. What Characteristics Account for the Great Success of Cnidarians? 3. Ability to proliferate by cloning

  13. What Characteristics Account for the Great Success of Cnidarians? 4. And to form polymorphic colonies Hydractinea

  14. What Characteristics Account for the Great Success of Cnidarians? 4. And to form polymorphic colonies Physalia Portuguese Man-O-War

  15. What Characteristics Account for the Great Success of Cnidarians? 5. Formidable prey-capture device Nematocyst Prey tissue Empty Cnidocyte

  16. What Characteristics Account for the Great Success of Cnidarians? 5. Formidable prey-capture device

  17. What Characteristics Account for the Great Success of Cnidarians? 6. Low Energy Demands

  18. Diversity of Cnidarians 3 Main Taxonomic classes Class Scyphozoa Class Anthozoa Class Hydrozoa Class Cubozoa contains a few jellyfish spp

  19. How is it that organisms as different as jellyfish, hydroids and anemones can be classified in the same phylum? Giant anemone

  20. Similarities of Polyp and Medusa

  21. Nutritive muscular cells Gland cells Epitheleo-muscular cells cnidocytes mesoglea

  22. Nerve Nets and Muscular System Mouth

  23. Epitheliomuscular Cells and gastromuscular cells Lacking mesoderm, but muscles derived from epithelial endodermal and ectodermal cells

  24. Characteristics of the Class Scyphozoa (Adaptations to a drifting, carnivorous lifestyle) About 200 species

  25. Hydromedusa for comparison • Small a few cm • Velum to aid in locomotion • Radial canals unbranched • Simple epidermal and endodermal nerve net • Nematocysts usually small without toxins

  26. Characteristics of the Scyphozoa mesoglea gastric pouch stomach gonad radial canal gastrodermis Radial canal mouth

  27. Characteristics of the Scyphozoa (Adaptations to a drifting, carnivorous lifestyle) Stomach Stomach G-V cavity more complex, adapted to subdue and digest larger and active prey G-V Canals Gastric Pouches MOUTH MANUBRIUM

  28. Characteristics of the Scyphozoa (Adaptations to a drifting, carnivorous lifestyle) G-V cavity more complex, adapted to subdue and digest larger and active prey

  29. Characteristics of the Scyphozoa mesoglea gastric pouch stomach gonad radial canal gastrodermis Radial canal mouth

  30. Coronal Muscles and swimming How is swimming pace, direction coordinated?

  31. How are the coronal muscles connected to the nervous system that includes: • Sensory neurons, motor neurons • Nerve net • - Inner and outer nerve rings • - Marginal ganglia associated with rhopalia that constitute a pacemaker

  32. To ganglia Characteristics of the Scyphozoa (Adaptations to a drifting, carnivorous lifestyle) The nervous system is more complex; unique sensory structures (than nerve net shared by all Cnidaria)

  33. Rhopalium (Digestive)

  34. Rhopalia are Intergrated with Nerve Rings in Box Jellies (Cubomedusa) Garm et al., 2006 Cell Tissue Research #325 EN: epidermal nerve GN: gastrodermal nerve RC: Ring Canal EN joins the nerve ring NCB: nerve cluster RN: ring nerve

  35. 24 eyes but no brain? Epidermal nerve of rhopalia Inner and outer nerve rings Marginal ganglia Nerve net Coronal muscles Epiheliomuscular system

  36. When did a Centralized Nervous System Evolve? “Conventional” view Marlow et al., 2009, Developmental Neurobiology

  37. Cnidarian nerve net e.g. Hydra

  38. “Sub-functionalized” N.S. Sea Anemone Nematostella

  39. Nerve rings are Core of CNS in medusae --Concentrations of hundreds of axons in parallel form coupled nerve rings. Having an annular form rather than a large ganglion does not make it less centralized. -- The annular configuration is a function of radial symmetry Mackie, 2004. Neurosignals #13

More Related