Ch 27- Worm and Mollusks
• Welcome to Discovery Education Player
• Characteristics of flatworms
– Soft, flattened worms with tissues and internal organ
system
– Simplest animals to have three embryonic germ layers
– Bilateral symmetry
– Cephalization
– Acoelomates
• Phylum Platyhelminthes
• Coelom- fluid filled coelom forms between
tissues of flatworms
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No circulatory or respiratory systems
Pharynx- muscular tube that extends out for feeding
Flame cells- specialized cells that remove wastes from body
Ganglia- group of nerve cells that controls nervous system
Eyespot- group of cells that can detect changes in amount
of light in their environment
• Most are hermaphrodites that reproduce sexually
– Hermaphrodite- individual with both male and female
reproductive organs
• Some reproduce asexually by fission- organism splits into 2
• Muscle cells and cilia to move
Groups of flatworms
• Turbellarians- class Turbellaria
– Free-living
– Most live in marine or fresh water- bottom dwellers
• Flukes- class Trematoda
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Parasitic flatworms
Infect internal organs of host
No eye spots
Hermaphrodites
Burrow into intestines and release embryos into
intestine- passed out with feces
• Tapeworms- class Cestoda
– Long, flat, parasitic worms
– Adapted to life inside of intestines of host
– Scolex enables worm to hook to host
– Proglottids- segments that make up body
• Contain both male and female reproductive organs
– No eyespots
– No mouth, grastrovascular cavity, or digestive
organs
– Hermaphrodites
– Raw or undercooked food
Sec 2- Roundworms
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Phylum Nematoda
Unsegmented worms
Bilateral
Long slender bodies
Cuticle
Most are free living
Have pseudocoeloms and digestive systems with 2
openings- mouth and anus
– Pseudocoelom- false coelom, only partial with tissue
dervived from mesoderm
• Types include hookworms, trichinella, pinworms
• Parasitic roundworms include trichinella, filarial, ascarid,
and hookworms
• Trichinosis- disease caused by trichinella, live in hosts
intestines
– Uncooked pork
• Filarial worms- live in blood and lymph vessels of birds and
mammals
– Tropical regions of Asia, transmitted by biting mosquitos
– Elephantiasis
• Ascarid worms- live in host’s small intestine
– Commonly spread by eating vegetables not washed properly
– Can reach 50 cm
• Hookworms- live in host’s intestines
– Burrow into skin and enter bloodstream
– Suck on host’s blood
Sec 3- Annelids
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Phylum Annelida
Earthworms
True coelom lined with tissue derived from mesoderm
Closed circulatory system
Reproduce sexually, separate sexes and hermaphrodites
Long and narrow segmented bodies
– Septa- internal walls that separates the body into segments
– Setae- bristles that are attached to each segment
• Nephridia- excretory organs that excrete nitrogen
containing wastes
• Clitellum- band of thickened, specialized segments that
secretes mucous that contains eggs and sperm
Groups of Annelids
• Oligochaetes- class Oligochaeta
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Earthworms and relatives
Typically have streamline bodies
Relatively few setae compared to polychaetes
Most live in soil or freshwater
• Leeches- class Hirudinea
– External parasites that suck blood and body fluids of their host
– Live in moist habitats in tropical countries
• Polychaetes- class Polychaeta
– Sandworms, bloodworms, and relatives
– Marine annelids
– Have paired, paddlelike appendages tipped with setae
Sec 4- Mollusks
• Phylum Mollusca
– One of oldest and most diverse phyla
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Soft-bodied animals
Usually have internal or external shell
Include snails, slugs, clams, squids, and octopi
Trochophore- free-swimming larval stage
– Characteristic of aquatic mollusks and annelids
Form and function in mollusks
• Body plan of most mollusks
– Foot, mantle, shell, visceral mass
• Radula- flexible tongue shaped structure used for
feeding by snails and slugs
• Octopi use sharp jaws to eat prey
• Clams, oysters, and scallops are filter feeders
– Siphon- tubelike structure through which water enters
and leaves the body
• Open circulatory system
Groups of Mollusks
• Gastropods- class Gastropoda
– Pond snails, land slugs, sea butterflies, sea hares
– Shell-less or single shelled mollusks
– Move by using muscular foot located on ventral side
• Bivalves- class Bivalvia
– 2 shells that are held together by one or two powerful muscles
– Clams, oysters, mussels, and scallops
• Cephalopods- class Cephalopoda
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Most active
Octopi, squids, cuttlefishes, nautiluses
Soft bodied mollusks in which head is attached to single foot
Foot is divided into tentacles or arms