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Poriferans Phylum Porifera • • • • • • • • Phylum Porifera – “pore-bearers” Sponges Tiny openings, pores, all over the body Cambrian Period – 540 m.y.a.; oldest and simplest animals Adults are sessile – attached to a single spot Heterotrophic, multicellular, no cell walls, few specialized cells No mouth or gut, no tissues, no organ systems Evolutionary dead end Form and Function of Sponges • Movement of water through sponge provides for feeding, respiration, circulation, and excretion • Body plan – Asymmetrical “water pump” – body forms wall around central cavity, where water is continuously pumped – Choanocytes (aka Collar Cells) – create currents with flagella – Most have an osculum – large exit hole at top of sponge Form and Function of Sponges (continued) • Simple skeletons – Spicules – sponge “bones” made of calcium carbonate (CaCO3) or silica (SiO2) – these are in hard sponges – Archaeocytes – make spicules – Softer sponges have skeletons made of spongin – these are used as natural bath sponges Sponge Anatomy Water flow Osculum Central cavity Pores Choanocyte Spicule Pore cell Pore Epidermal cell Archaeocyte Feeding in Sponges • Filter feeders – sift microscopic food particles from water • Digestion is intracellular • Food particles engulfed by choanocytes lining body cavity by endocytosis • Food may be digested or passed on to archaeocytes • Archaeocytes digest food and wander around to other cells delivering nutrients Respiration, Circulation, and Excretion in Sponges • Rely on movement of water through bodies to provide simple mechanism for respiration, circulation, and excretion • Diffusion is important for sponges Response in Sponges • No nervous system, but can produce toxins Reproduction in Sponges • Sexually or asexually • Sexual – most sponges have eggs and sperm in one sponge – Eggs held in body wall – Sperm released into water – Eggs and sperm produced at different times within sponge – Sperm absorbed by archaeocytes and carried to eggs – Fertilized eggs forms zygote which develops into larvae, which are planktonic and motile. Eventually, larvae settle down to bottom and grow into a new sponge. Sponge Life Cycle MEIOSIS Sperm from a sponge are released into the surrounding water. Water currents carry the sperm to other sponges. Haploid (N) Diploid (2N) New sponge Sperm (N) Mature sponge (2N) Egg (N) Swimming larva The zygote develops into a free-swimming larva. Water currents carry the larva until it attaches to a surface and grows into a new sponge. Larva (2N) Sperm enter another sponge through pores. The sperm are carried to eggs inside the body wall. Sperm fertilize eggs. FERTILIZATION Reproduction in Sponges (continued) • Asexual – Gemmules – collections of archaeocytes surrounded by spicules that can survive freezing and heat – Conditions favorable, gemmule grows into new sponge – Budding – part of sponge breaks off, settles, grows into new sponge Ecology of Sponges • Form sponge “habitats” for worms, shrimps, snails, and starfish • Symbionts with bacteria, blue-green bacteria, or plant-like protists • Natural bath sponges • Provide toxins that fight bacteria, viruses, leukemia, and herpes Summary of Cell Specialization in Sponges • Choanocytes – Create water currents with flagella – Capture food • Archaeocytes – Make spicules – Deliver nutrients to sponge – Assist with reproduction Examples of Sponges Cnidarians Cnidarians • Phylum Cnidaria – cnidocytes – stinging cells • Jellyfish, sea anemone, coral • Soft-bodied, carnivorous animals with stinging tentacles arranged around their mouth • Simplest animals to have body symmetry and specialized tissues • Within each cnidocyte is a nematocyst (poisonfilled stinging structure used for food capture and protection) Form and Function of Cnidarians • Only a few cells thick and simple body systems • Body plan • Radial symmetry with 2 possible body forms: – Polyp – sessile and flower-like – Medusa – motile and bell-shaped • Three layers of cells – Gastroderm – inner lining of gastrovascular cavity digestion – Mesoglea – middle layer – can be a thin or thick layer – Epidermis – outer layer Body Forms of Cnidarians Epidermis Mesoglea Gastroderm Tentacles Mesoglea Gastrovascular cavity Mouth/anus Mouth/anus Gastrovascular cavity Tentacles Medusa Polyp Feeding in Cnidarians • Nematocysts – located on tentacles; tiny spring-loaded harpoons • Food pushed into mouth by tentacles • Food digested and absorbed by diffusion Respiration, Circulation, and Excretion in Cnidarians • Respiration and wastes eliminated by diffusion through body wall • No organized internal transport network or excretory system Response in Cnidarians • No organized central nervous system (CNS) • Simple nerve nets – loosely organized network of nerve cells allowing detection of stimuli • Statocysts – sensory cells for balance • Ocelli – eyespots detect light Movement in Cnidarians • Hydrostatic skeleton – layer of longitudinal muscles, together with the water in the gastrovascular cavity, allow movement • Epidermal cells act as muscles Reproduction in Cnidarians • Sexual and asexual • Asexual – polyps reproduce by budding • Sexual – external fertilization in the water Polyp Larvae Asexual Reproduction Zygote Medusa Sexual Reproduction Groups of Cnidarians • Includes hydras and their relatives, jellyfishes, sea anemones, and corals Class Hydrozoa – Hydras and Other Relatives • • • • Long polyp stage Short medusa stage Hydra – fresh-water – no medusa Portuguese Man-O-War – floating colony contains specialized polyps; one polyp is enlarged and full of air to keep the animal afloat, the other polyps are for feeding and reproduction Examples of Hydrozoans Portuguese Man-O-War Colonial Hydrozoan Green Hydra Class Scyphozoa – Jellyfish • • • • • Same life-cycle as hydrozoans Medusa – long-lived Lion’s Mane Reproduce sexually Some very toxic and even deadly Examples of Scyphozoans Class Anthozoa – Sea Anemones and Corals • • • • Only polyp life stage Colonial Sexual and asexual reproduction Corals – reef builders and symbionts with photosynthetic algae • Skeleton of calcium carbonate (CaCO3) • Colony grows slowly and lives for thousands of years Examples of Anthozoans Ecology of Corals • Great Barrier Reef – 2,000km long, 80 km wide • Sea anemone and clown fish – mutualism • Coral – habitat for many animals – Protect land from wave action – Building blocks – Jewelry – Anti-cancer drugs – In danger due to human activity