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Chapter 8 Key Concepts • Sponges are asymmetric, sessile animals that filter food from the water circulating through their bodies. • Sponges provide habitats for other animals. • Cnidarians and ctenophores exhibit radial symmetry. • Cnidarians possess a highly specialized stinging cell used to capture prey and for protection. • Most marine animals exhibit bilateral symmetry. • Turbellarians are free-living flatworms; flukes and tapeworms are parasitic flatworms. • Ribbon worms are marine predators that somewhat resemble flatworms. • Phoronids, bryozoans and brachiopods have a specialized feeding structure called a lophophore. What Are Animals? • Animals: • multicellular • eukaryotic cells without cell walls • cannot produce their own food • invertebrates • vertebrates • most marine animals are invertebrates Sponges • Phylum Porifera • Basic characteristics: – simple – asymmetric – sessile Sponge Structure and Function • Nutrition and digestion – suspension/filter feeders – pinocytes and archaeocytes – collar cells • Reproduction in sponges – asexual reproduction • budding • fragmentation – sexual reproduction • most hermaphrodites • eggs from archaeocytes and sperm from modified collar cells • larval stage is called a planktonic amphiblastula Ecological Roles of Sponges • • • • Competition – corals and bryozoans Predator-prey relationships – few species eat sponges • spicules • chemical deterrents Symbiotic relationships – mutualistic or commensalistic hosts – organisms live within the canals Sponges and nutrient cycling – boring sponges Cnidarians: Animals with Stinging Cells • Include jellyfish, hydroids, corals and sea anemones • cnidocytes Stinging Cells • Cnida – nematocysts • Dangerous species – Portuguese man-of-war – box jellyfish Types of Cnidarians • Hydrozoans – mostly colonial – colonial forms contain 2 types of polyp: • gastrozooid • gonangium – hydrocorals secrete a calcareous skeleton – some produce floating colonies • Jellyfish – scyphozoans—true jellyfish (class Scyphozoa) • plankton • medusa is predominant • photoreceptors • Box jellyfish – box jellyfish (class Cubozoa) • box-shaped bells • relatively strong swimmers • tropical • voracious predators, primarily of fish • Anthozoans (class Anthozoa) – include sea anemones, corals and gorgonians – sea anemones • benthic • • • gastrovascular cavity divided • though sessile, many can change locations Anthozoans (class Anthozoa) – coral animals • polyps secrete a skeleton • scleractinian corals • form reefs Anthozoans (class Anthozoa) – soft corals • polyps that form plant-like colonies Nutrition and Digestion • Gastrovascular cavity – digestion and transport – waste out mouth • Many suspension feeders • Jellyfish and box jellyfish are carnivorous • Sea anemones generally feed on invertebrates, some large species feed on fish, shallow water species have symbiotic algae Reproduction • Hydrozoans – asexual polyp stage and sexual medusa stage • Scyphozoans • Anthozoans – asexual reproduction IS COMMON • pedal laceration • fission • budding – sexual reproduction • male and female forms, gametes are released • planula larva Ecological Relationships of Cnidarians • Predator-prey relationships – cnidarians are predators – stinging cells discourage predation – sea turtles, some fish and molluscs prey on hydrozoans and jellyfish • Habitat formation – coral polyps form complex 3-dimensional structures inhabited by thousands of other organisms – coral reefs provide a solid surface for attachment, places for pelagic animals to rest and hide and buffer waves and storms • Symbiotic relationships – Portuguese man-of-war and man-of-war fish – reef-forming corals and zooxanthellae – sea anemones: • clownfish • the hermit crab Ctenophores • Planktonic, nearly transparent • Ctenophore structure – 8 rows of comb plates – radial symmetry – lack stinging cells – bioluminescent • Digestion and nutrition – feeds on plankton, larval fish and fish eggs – branched tentacles, adhesive cells, jellyfish stingers to capture prey • Reproduction – most hermaphroditic – fertilization in water or eggs may be brooded – cydippid larva • Ecological Role – can effect zooplankton abundance directly and fish populations by preying on fish larvae and eggs The Evolution Of Bilateral Symmetry • Bilateral symmetry – allowed for streamline body shape – cephalization Flatworms • Have flattened, bilaterally symmetrical bodies • Turbellarian flatworms • Flukes and tapeworms • Types of flatworm – turbellarians are mostly pelagic, and are members of meiofauna – turbellarians have sensory receptors to detect light, chemicals, movement and to maintain balance – flukes usually have complex life cycles – tapeworms live in the host’s digestive tract • Reproduction – can reproduce asexually – sexual reproduction • reciprocal copulation • turbellarians produce few eggs • parasitic flatworms produce 10 to 100 thousand times more eggs than turbellarians • Ecological role of flatworms – Turbellarians: – • turbellarians funnel nutrients to higher trophic levels • prey for higher-level consumers Parasitic flatworms: • can regulate population size by lowering fitness of host Ribbon Worms • Phylum Nemertea – most are benthic – sexes are separate, fertilization external – carnivorous – capture prey with proboscis • Ecological role of ribbon worms – prey organisms for higher consumers – burrowing in sediment moves nutrients to surface – abandoned burrows can serve as habitat Lophophorates • sessile animals that lack a distinct head • lophophore • 3 phyla of lophophorates: – Phoronida – Ectoprocta – Brachiopoda Phoronids • Secrete a tube of leathery protein or chitin • Catch plankton and detritus • Can reproduce sexually or asexually • Have a planktonic larval stage Bryozoans • live colonies on rocks, shell, algae, mangroves • one of the most abundant marine epiphytic animals • Colonies are composed of zooids • most are hermaphroditic brooders • Larvae are planktonic, settle to form new colonies Brachiopods • Most brachiopods are benthic, live in shallow water • Have mollusc-like, bivalve shells – valves differ in size and shape, and are dorsal and ventral – a pedicle (fleshy stalk) attaches the shell or is buried • Gather detritus/algae with lophophore • Generally have separate sexes; larvae are planktonic and settle in 24-30 hrs. Ecological Roles of Lophophorates • • • As a group, they are filter feeders Food for many invertebrates, especially molluscs and crustaceans Largely responsible for fouling ship bottoms