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

• 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– 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

• 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

• 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– 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

• 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– Most active– Octopi, squids, cuttlefishes, nautiluses– Soft bodied mollusks in which head is attached to single foot– Foot is divided into tentacles or arms