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4/28/11 Chapter 9! Multicellular Levels of Organization! Porifera & Cnidaria! I. Evolutionary Perspective! II. Phylum Porifera! Multicellular Organisms have been around for about 600 million years! 2 Hypotheses! Colonial Characteristics of Sponges (~9000 species)! • Pinacocytes! • Mesenchyme! • Choanocytes! Hypothesis! • Colonial protists became specialized and interdependent with one another! Syncytial Hypothesis! • Formation of plasma membranes within a large, multicnucleate protist! Asymmetrical! Three Cell Types! Central cavity or a series of branching chambers for water flow! No tissues or organs! Filter feeders! Body has pores (ostia)! Skeleton of spicules! 3 Classes of Phylum Porifera! Class Calcarea! Class Spicules: • Fused into a lattice pattern, have six rays! • Made of Silica! Body Forms! Examples: Grantia sponges! Class Demospongiae! Forms! • Sycon, leucon! • Ascon, leucon, sycon! Examples: Class Demospongiae! 1 Spicules:! ! • Needle-shaped w/3 or 4 rays! • Made of Calcium carbonate! Body Hexactinellida! Marine! Marine! Glass sponges found in tropical waters! Family of freshwater sponges! The rest are marine! Spicules:! • Made of silica or spongin or both! • Needle shaped with 4 rays! Body Form: ! • Leucon! Examples: Spongillidae and bath sponges! III. Cell Types, Body Wall & Skeleton! Outer surface! Covered by pinacocytes (thin, flat cells)! Some are specialized porocytes (regulate water flow)! Middle layer! Called the mesohyl-jellylike layer! Has mesenchyme cells that resemble amoeba! • Move about in the mesohyl and used for reproduction, transporting and storing food, secreting skeletal elements! Inner Chamber! Lined with choanocytes! • Cells with a collar that have flagella for feeding and creating a current for water flow! Skeleton! Formed of spicules ! • Can be made of calcium carbonate, silica, or spongin! 1 4/28/11 IV. Water Currents and Body Forms! Ascon! Simplest form! Vase like! Choanocytes directly line the spongocoel! Sycon! Leucon! Sponge wall is folded! Water enters through dermal pores! Dermal pores lead to radial canals! Choanocytes line the radial canals! V. Feeding! Most Complex! Extensively branched canal system! Water enters through incurrent canals that lead to choanocytes! Water leaves through excurrent canals! No spongocoel! Have greater filtering capabilities! VI. Reproduction! Choanocytes filter particles from the water! Water passes through the collar near the base of the cell and food is trapped! Food is then moved along microvilli to a food vacuole and broken down by lysosomes! Digested food is passed where needed by amoeboid cells! Waste products are removed through diffusion! Sexual! Monoecious Asexual! (both sexes in the same individual)! and eggs are released through the ostia! Fertilization occurs in the water and develop into larvae! Larvae attach to the substrate and grow into new sponges! Sperm VII. Phylum Cnidaria (Jellyfish)! VIII. 3 Classes of Phylum Cnidaria! Characteristics Class of Jellyfish! Radial symmetry! Gelatinous mesoglea between the epidermal and gastrodermal tissue layers! Gastrovascular cavity! Nerve net for the nervous system! Specialized cells called cnidocytes! • Used for defense, feeding, and attachment! Form gemmules ! are filled with ameoboid cells and are released in large quantities in the winter! In spring the cells are released and grow into a sponge! These Class Hydrozoa! Hydrozoa! Epidermis has cnidocytes! are produced in the epidmeris and released outside body! Mostly marine, some freshwater! Examples: Hydra, Obelia, Gonioneums, Physalia! Have tentacles! Gametes 2 4/28/11 Class Scyphozoa - “True Jellyfish”! Class Scyphozoa! Medusa is dominant! Gametes released from gastrodermis into gastrovascular cavity! Marine! Examples: Aurelia! Class Cubozoa! Class Cubozoa! Medusa is dominant! is cube shaped! Tentacles hang from each corner! Marine! Examples: Chironex “Sea Wasp”! Medusa Class Anthozoa - Sea Anemones & Coral! Class Anthozoa! Have perfect radial symmetry! Polyp stage is dominant! Limited locomotion - glide on pedal disks! Can be solitary or colonial! Gametes released from gastrodermis! Examples: Sea anemones and stony corals! Body Wall and Nematocysts! Alternation of Generations! Has two body tissue layers - ectoderm and endoderm! Ectoderm! Gives rise to the epidermis! Forms the gastrodermis! Polyp and medusa! Polyp! Mesoglea! Endoderm! Most Cnidarians have two body forms in their life time! Usually asexual and sessile! Attaches to substrate at aboral end! Has a mouth surrounded by tentacles! Medusa! Shaped like a bell with tentacles hanging from the edges! Free swimming ! Dioecious - it is either male or femlae! Reproduction! Most species are dioecious! fertilization a free-swimming larva called planula is formed! Planula attaches to a substrate and develops into a polyp! Polyps bud and form medusa, which may swim away! After 3 4/28/11 Maintenance Functions! All have a gastrovascular cavity! Have nematocysts! Hydrostatic skeleton! Functions for digestion, gas exchange, waste excretion, discharge of gametes! Water is held in body cavities and acts as a support system! Phylum Ctenophora! Characteristics! Stinging cells on tentacles that allow them to capture prey (small fish and crustaceans)! Nerve Net! Phylum Ctenophora! Biradial symmetry! Jelly-like mesoglea between epidermis and gastrodermis! True muscle cells! Gastrovascular cavity! Nerve net! Colloblasts - adhesive cells capture prey! Eight rows of cilia called comb rows for movement! Examples: Comb Jellies! Conducts nerve impulses around the body! 4
