Platyhelminthes
Kingdom: Animal
Phylum: Platyhelminthes
Class: Turbella
Class: Trematoda
Class: Cestoda
General Characteristics
aka. Flatworms
_______________________
Least complex worms
14,500 species
Marine, freshwater, moist terrestrial environments
Body Structure
Bilateral symmetry
___________________: have a clearly-defined anterior end, characteristic of
motile animals, implies that the nervous tissue is
concentrated at the anterior end
___________________: Body wall consists of three cellular layers
Acoelomate: No body cavity, spaces between internal organs are filled
Digestion
___________________
Mouth, but no anal opening
Nervous system
Some species have a nerve net: simple nervous system where the nerves are
spread over the organisms like a net
Others have a very simple nervous system with two nerve chords
Asexual Reproduction
Budding: can re-grow body parts or an entire new body (regeneration)
Most flatworms can grow after being cut in two
Sexual Reproduction
Hermaphrodites (have both eggs and sperm)  swap DNA
Life Cycle
Not fast moving
Sessile species usually parasites
Latch onto host’s insides and absorb nutrients from inside the host
Platyhelmithes Classes
Class: Tubellaria (Planarians)
Dugesia tigrina (Planaria)
General Characteristics
Free living
Mostly aquatic
Marine, freshwater, bottom dwellers, humid terrestrial forests
(live in algae masses or under stones)
Body Structure
Elongated, with triangular shaped head
Two anterior eye spots
Mouths in the middle of the ventral side
Planarian Nervous System
Ganglion: Located at head, receives messages from eyespots and sensory pits &
can communicate with the rest of the body along the nerve chords
Two nerve chords run down length of body, has sensory pits that detect chemicals and
movement in water
Two sensors that detect light (eyespots)
How Planaria Eat
1st Pharynx
Tubelike, muscular organ, extends out of mouth, sucks in food
2nd Gastrovascular cavity
Food broken up by enzymes
rd
3 Phagocytosis
Cells lining GC absorb nutrients
th
4 Cellular Respiration
Individual cells digest food
th
5 Waste Removal
Flame cells: remove waste through pores on body surface by using cilia
planaria
Class: Trematoda (flukes)
Fasciola hepatica (Sheep liver fluke), Fasciola buski (Human liver fluke)
General Characteristics
All are parasites
Mostly endoparasites (inside)
Most hosts are vertebrate (humans and sheep)
Immature stages are often harbored in invertebrates (slug)
Life Cycle
1. The eggs pass from the host in feces.
2. Eggs reach water, they hatch into free-swimming larva.
3. The larva penetrate a snail, or other mollusk.
4. Continue to mature and escape from
5. The mollusk into the water.
Prevention
Do not drink, swim or stand in snail infested water.
Class: Cestoda (tapeworms)
Teania pisiformis (dog and cat tapeworms), Teania solium (human tape worm)
General Characteristics
All are endoparasites
Adult worms live in the intestines of vertebrate hosts
Larvae live in tissues of alternate hosts
Body Structure
No mouth or digestive track; food is absorbed from host directly through body wall
Mostly slender and elongated with a flat body of many short segments
Scolex
anterior segment, knob-like, covered in suckers, cften covered in hooks
Stroblia
Remainder of tapeworm
Composed of Proglottids (flattened segments, mostly ovaries and testies)
Regenerates easily, just need a proglottid to break off  a new tapeworm
Life Cycle
1. Ingest the fertilized eggs in water or in undercooked meat
2. Larva develop in the intestine
3. Secrete sperm and eggs which are fertilized and passed out in feces.
Prevention
Drink clean water
Thoroughly cook meat