Presentation on theme: "Chapter 9 Multicellular and Tissue Levels of Organization"— Presentation transcript:
1Chapter 9 Multicellular and Tissue Levels of Organization Phylum Porifera – The SpongesZoology
2Origins of Multicellularity Why become multicellular?Division of labor, specialized cells with specific functions.Two Hypotheses:Colonial Hypothesis – a dividing protist remained together.Syncytial Hypothesis – formation of plasma membranes in a protist may have produced a small, multicellular organism.
3The common ancestor of living animals May have lived 1.2 billion–800 million years agoMay have resembled modern choanoflagellates, protists that are the closest living relatives of animals.Identical to a type of sponge cell – choanocytes – used in feeding.Single cellStalk
4Characteristics of Porifera Porifera – means “pore bearing”9,000 + species, mostly marineAsymmetrical Body PlanThree Cell Types: pinococytes, mesenchyme cells, and choanocytesWater canal systemCellular Organization, but no tissue or organsImages courtesy and copyright Dr. John Hooper, Queensland Museum
5Porifera Diversity – Three Classes Class DemospongiaeClass Hexactinellida, Staurocalyptus sp.Class Calcarea – composed of calciteImages Courtesy:http://www.palaeontologie.geo.lmu.de/molpal/calcarea_introduction.html
6More than Just Cute! Have a division of labor Pinacocytes – thin, flat cells that line outer surface, may contract and change shape of sponge or regulate water entry – porocyte.Mesohyl – jellylike layer below pinacotye layer.Mesenchyme Cells – ameboid cells moving about in mesohyl; for reproduction, secreting structures, food transport and storage.Choanocytes – flagellated cells below mesohyl that line inner chamber(s); create water current and filter microscopic food.
10Other species make a fibrous protein of collagen - spongin Some species make spicules – thorn-like projections that provide structural support and protection; made of calcium carbonate by ameboid cells.Other species make a fibrous protein of collagen - sponginSpicules
12Water Currents for Everything! Choanocytes use their flagella to create water currents through external pores called – ostia (sing. ostium,); incurrent pores.Bring food (bacteria, protists, etc.) and oxygen and remove metabolic wastes from the center of the sponge – spongocoel.Choanocytes use collar-like rings to filter food.Wastes and water flow out a central osculum (plural, oscula); an excurrent pore.
151. Ascon Body FormSimplest canal system with a central spongocoel lined with choanocytes and with many ostia opening directly into spongocoelLeast common
162. Sycon Body Form Sponge wall is folded Water enters via dermal pores Canal system with a central spongocoel into which many radial canals empty.Choanocytes line radial canals
173. Leucon Body FormBranched incurrent canals lead to choanocyte-lined chambersNo spongocoelIncreased surface area = larger volume of water movementMost common
18Let’s Eat! Choanocytes filter microscopic food and trap in collar. Placed into food vacuole and digested by lysosomes.Digested food is passed to amoeboid cells for transport to other cells – beginnings of specialization.
19The Importance of Water Currents Respiration (gas exchange), Metabolism, and Excretion all done by direct diffusion with water.No nervous system – no responsiveness.Defenses – may produce some irritating chemicals if touched; chemical defense against predators, fish, sea stars, etc.
20ReproductionSponges are monoecious (both sexes in the same individual – hermaphrodite).Do not self-fertilize. Why?Choanocytes become sperm.Other choanocytes and amoeboid cells become eggs.Released from oscula and exteranl fertilization.Larvae are free-swimming.
21Free-swimming larvae settle to the bottom and …. …become sessile (attached to the bottom) adults
22Alternatives to SexAsexual reproduction from internal, resistant capsules – gemmules.Gemmules – are masses of ameboid cells that are released when parent dies.Dormant stage - resistant to freezing and drying.Pieces broken off can become a new sponge – fragmentation.Grow new pieces – budding.
23And their good to eat, too! Sponge Cake, Anyone?