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