Notes 29-3

Flatworms and Roundworms

Flatworm Characteristics

--Flat bodies (gases move by diffusion)
--bilateral symmetry
--gastrovascular cavity
--some flatworms are parasitic, some are freeliving
--they have anterior and posterior heads and exhibit cephalization

Types of Flatworms (planarian, tapeworm, fluke)

Planarian (also known as Dugesia)--lives in freshwater
--mostly a scavenger, also feeds on protists
--hermaphrodites
--has a simple brain (ganglia) and nervous system, plus 2 eyespots
(see handout on planarian)
--they can regenerate (regrow parts)

Anatomy of the Planarian

Brain (ganglia) - planarian can process information about their environement
Pharynx - used for suckling food in (the mouth is at the end of the pharynx)
Eyespot - simple eye, can detect light
Flame cells - located along the lateral edges, used for excretion
Intestine - digestion (does not have an anus)

Tapeworms
--parasitic worms that live in the digestive system
--they have segmented bodies (each segment is called a proglottid)
--each proglottid is a reproductive organ
--tapeworms can grow very long (40 feet!)
--attach to the intestine with hooks and suckers on the head
--do not have well developed digestive systems

Flukes
--most have complex life cycles involving more than one host
--Schistosoma (blood fluke) spends part of its life in a snail, humans get infected when they wade in the water containing the snails, the larva then invade the human's blood vessels
--eggs are passed thru human feces into water where the snail is infected
(see fig 29-16)

Roundworms

--have a complete digestive tract

Ascaris -common roundworm infection in humans and dogs
Trichinella -roundworms that invade muscle tissue, get by eating undercooked pork
Vinegar eel - free living roundworm