Download Chapter 8 Key Concepts • Sponges are asymmetric, sessile animals

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