Platyhelminthes

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• Platyhelminthes
• Flatworms - Dorsoventrally flattened
• Simplest bilaterally symmetrical organisms
• First organs and organ systems
• Central nervous system
• Simple brain coordinates muscle movements
• Incomplete digestive system
• Mouth but no anus
• Similar to Cnidaria and Ctenophora
• Mesoderm
• Cell layer between endoderm and ectoderm
• Gives rise to muscles, reproductive system

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• Platyhelminthes
• Turbellaria
• Mostly free-living carnivorous species
• Most commonly seen (Why?)
• Some live as commensal animals inside other
  invertebrates (oysters, crabs, etc.)

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• Platyhelminthes
• Trematoda (Flukes)
• Most species (6000)
• Parasitic Feed on tissues, blood, gut contents
• Complex life cycles
• Adults live in vertebrate host (fish, whale,
  bird)
• Larvae may inhabit invertebrates (intermediate
  hosts)
• Vertebrate eats intermediate host (clam, snail,
  etc.)
• Cestoda (Tapeworms)
• Parasitic
• Live in vertebrate intestines
• Head attaches to intestine wall with suckers or
  hooks
• Gutless absorb nutrients through body wall
• May reach 50 feet!! (sperm whales)

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• Nemertea
• Ribbon worms
• Cosmopolitan
• Most common in shallow, temperate regions
• Complete digestive tract
• Mouth and anus
• Circulatory system
• Use long, fleshy proboscis to capture prey
• Feed on crustaceans and worms
• May be cryptic or conspicuous
• Can reach 30 m in length!!

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• Lophophorates
• Three phyla all animals possess lophophore
• Ciliated hollow tentacles arranged in a horseshoe
• Suspension feeders
• Bilateral symmetry, coelom (body cavity),
  U-shaped gut
• Ectoprocta Bryozoans
• Colonies consist of interconnected individual
  zooids
• Encrusting and lacy forms (CaCO3 tests)
• Retractable lophophore
• Phoronida Phoronids, Horseshoe Worms
• Worm-shaped
• Agglutinated sediment tubes attached to hard
  substrate in shallow water
• Brachiopoda Lamp Shells
• Abundant in fossil record
• Superficially resemble clams, but shells are
  dorsal-ventral, not left-right as in mollusks
• Many attached to substrate with pedicle (short
  stalk)

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Bryozoans
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• Lophophorates
• Three phyla all animals possess lophophore
• Ciliated hollow tentacles arranged in a horseshoe
• Suspension feeders
• Bilateral symmetry, coelom (body cavity),
  U-shaped gut
• Ectoprocta Bryozoans
• Colonies consist of interconnected individual
  zooids
• Encrusting and lacy forms (CaCO3 tests)
• Retractable lophophore
• Phoronida Phoronids, Horseshoe Worms
• Worm-shaped
• Agglutinated sediment tubes attached to hard
  substrate in shallow water
• Brachiopoda Lamp Shells
• Abundant in fossil record
• Superficially resemble clams, but shells are
  dorsal-ventral, not left-right as in mollusks
• Many attached to substrate with pedicle (short
  stalk)

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• Lophophorates
• Three phyla all animals possess lophophore
• Ciliated hollow tentacles arranged in a horseshoe
• Suspension feeders
• Bilateral symmetry, coelom (body cavity),
  U-shaped gut
• Ectoprocta Bryozoans
• Colonies consist of interconnected individual
  zooids
• Encrusting and lacy forms (CaCO3 tests)
• Retractable lophophore
• Phoronida Phoronids, Horseshoe Worms
• Worm-shaped
• Agglutinated sediment tubes attached to hard
  substrate in shallow water
• Brachiopoda Lamp Shells
• Abundant in fossil record
• Superficially resemble clams, but shells are
  dorsal-ventral, not left-right as in mollusks
• Many attached to substrate with pedicle (short
  stalk)

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• Corals
• Biology
• Phylum Cnidaria, Class Anthozoa (most)
• Lack medusa stage
• Hermatypic (reef building) corals produce
  skeletons made of calcium carbonate
• Most contain mutualistic zooxanthellae (provide
  nutrition enhance calcium carbonate deposition)
• Many growth forms

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• Corals
• Biology
• Reproduction
• Sexual Most broadcast spawners some brooders
• Polyp ? Planula (planktonic larva) ? Polyp
• Asexual Fragmentation (can be very important)
• All polyps in a colony genetically identical

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Fig. 15-4
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• Coral Reefs
• Distribution
• Living reefs 600,000 km2 (0.17 of sea floor)
• Great Barrier Reef Largest
• gt2000 km long
• Up to 145 km wide
• Visible from space

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• Coral Reefs
• Conditions
• Substrate
• Primarily in areas with hard substrate
• Light - Bright (Why?)
• Rarely develop in water gt 50 m deep
• Continental shelves, around islands, tops of
  seamounts
• Temperature
• Mean annual water temperature gt 20 oC
• Best development at 23-25 oC

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Distribution of Coral Reefs
Fig. 15-14
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• Coral Reefs
• Conditions
• Temperature
• Too warm also problematic
• Can cause bleaching and eventually death
• Bleaching events often occur during periods of
  unusually warm water
• Extreme low tide
• El Niño event
• Corals live near their upper thermal tolerance
  levels
• Corals from warmer waters have higher thermal
  tolerance levels

Fig. 15-33
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• Coral Reefs
• Conditions
• Salinity
• Reefs tend to be absent or poorly developed near
  mouths of rivers
• Sediments
• Turbidity reduces light levels
• Sediments can smother corals
• Pollution
• Corals sensitive to pesticides and other
  chemicals
• Fertilizers support growth of algae that smother
  corals
• Most corals grow in areas with low nutrient
  levels
• Tidal Regime
• Most corals intolerant of prolonged exposure