I. 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

I. Platyhelminthes

A. Turbellaria• Mostly free-living carnivorous species• Most commonly seen (Why?)• Some live as commensal animals inside other

invertebrates (oysters, crabs, etc.)

I. Platyhelminthes

B. 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.)

C. 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)

II. 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!!

III. Lophophorates

• Three phyla – all animals possess lophophore• Ciliated hollow tentacles arranged in a horseshoe

• Suspension feeders• Bilateral symmetry, coelom (body cavity), U-shaped gut

A. Ectoprocta – Bryozoans• Colonies consist of interconnected individual zooids

• Encrusting and lacy forms (CaCO3 tests)• Retractable lophophore

B. Phoronida – Phoronids, Horseshoe Worms• Worm-shaped• Agglutinated sediment tubes attached to hard substrate in

shallow water

C. 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)

Bryozoans

III. Lophophorates

• Three phyla – all animals possess lophophore• Ciliated hollow tentacles arranged in a horseshoe

• Suspension feeders• Bilateral symmetry, coelom (body cavity), U-shaped gut

A. Ectoprocta – Bryozoans• Colonies consist of interconnected individual zooids

• Encrusting and lacy forms (CaCO3 tests)• Retractable lophophore

B. Phoronida – Phoronids, Horseshoe Worms• Worm-shaped• Agglutinated sediment tubes attached to hard substrate in

shallow water

C. 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)

III. Lophophorates

• Three phyla – all animals possess lophophore• Ciliated hollow tentacles arranged in a horseshoe

• Suspension feeders• Bilateral symmetry, coelom (body cavity), U-shaped gut

A. Ectoprocta – Bryozoans• Colonies consist of interconnected individual zooids

• Encrusting and lacy forms (CaCO3 tests)• Retractable lophophore

B. Phoronida – Phoronids, Horseshoe Worms• Worm-shaped• Agglutinated sediment tubes attached to hard substrate in

shallow water

C. 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)

IV. Corals

A. 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

IV. Corals

A. 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

Fig. 15-4

V. Coral Reefs

A. Distribution• Living reefs ~

600,000 km2 (0.17% of sea floor)

• Great Barrier Reef = Largest

• >2000 km long

• Up to 145 km wide

• Visible from space

V. Coral Reefs

B. Conditions1. Substrate

• Primarily in areas with hard substrate

2. Light - Bright (Why?)• Rarely develop in water > 50 m deep• Continental shelves, around islands, tops of

seamounts

3. Temperature• Mean annual water temperature > 20 oC• Best development at 23-25 oC

Fig. 15-14

Distribution of Coral Reefs

V. Coral Reefs

B. Conditions3. 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

V. Coral Reefs

B. Conditions4. Salinity

• Reefs tend to be absent or poorly developed near mouths of rivers

5. Sediments• Turbidity reduces light levels• Sediments can smother corals

6. 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

7. Tidal Regime• Most corals intolerant of prolonged exposure