Phylum: Platyhelminthes

Phylum: Platyhelminthes

• “flatworms”

• Examples: tapeworms, flukes, planarians

Traits

• Flattened, worm-like body

Traits

• Bilateral symmetry

Traits

• Cephalized – have a distinct head end with a concentration of sensory nerves and brain

Traits

• Ladder-like nervous system

Traits

• 3 cell layers

Traits

• Blind sac digestive system

Types

• Planarians – free living flatworms• Tapeworms – segmented parasitic flatworms• Flukes – non segmented parasitic flatworms

Planarian structure

• Ectoderm (epidermis) – outside layer of cells

• Endoderm – inside layer of cells

• Mesoderm – the middle layer of cells

Mesoderm

• Advantage – allows for the development of complex internal organs

• Disadvantage – since not every cell is in contact with the water, getting oxygen and getting rid of wastes is a problem

Planarian structure

• Eyespot – detects light but can’t see shapes and images

Planarian structure

• Flame cells – excretory structures, collect nitrogenous wastes and force them out of the body through a series of tubes

Planarian structure

• Digestive system – blind sac, branches a lot so no cell is very far from food

Movement

• Can glide on ventral cilia or use muscles to swim

Reproduction

• Asexual – by regeneration or binary fission

Binary Fission

Reproduction

• Sexual – hermaphrodites, must exchange sperm (mate) with another worm

Tapeworms

• Segmented parasitic flatworms

Advantages of parasitism

• Food is readily available• don’t waste energy through movement• protected from the environment

Disadvantages of parasitism

• If the host dies, they die• Must get offspring to another host• Must produce a lot of offspring

Tapeworm Structure

• Scolex – head of a tapeworm

Tapeworm Structure

• Hooks and suckers – attach the tapeworm to the host’s intestinal wall

Tapeworm Structure

• Neck – pinches off proglottids

Tapeworm Structure

• Proglottids – reproductive segments of a tapeworm

Tapeworm Structure

• Cuticle – non cellular outside layer that keeps them from being digested from the host’s enzymes

Tapeworm Infestations

Symptoms

• Weight loss and fatigue• Final diagnosis is from a stool sample

Cure

• Easy• Since they live in the intestines, the medicine

goes directly to them, then they are eliminated with the feces

Life Cycle

• Adults live in the human intestines, mate, eggs leave with the feces

• A pig ingests food or water contaminated with the eggs

• Eventually lodge and form cysts in pig’s muscle• A human eats poorly cooked pork and it starts

all over again

BEEF TAPEWORM LIFE CYCLE

1. eggs released

2. eggs on grass

3. eggs eaten

4. larvae migrate to muscle & form cysts

5. Uncooked meat in consumed

Cysts in contaminated pork

Prevention

• Cook meat well• Good sewage systems

Flukes

• Non segmented parasitic flatworms

Flukes

• Endoparasites – live inside the body

Cure?

• Very difficult• Since they live in liver, medicine doesn’t go

directly to them• If you do kill them, the body can’t eliminate

them easily

Sheep liver fluke

• Live in a sheep’s liver• Can clog the bile duct and possibly kill the

sheep

Alternation of hosts

• Need at least 2 separate hosts to complete its life cycle

Life cycle

• Adults live inside the sheep’s liver, mate, eggs leave with feces

• Hatch into larvae which enter snails, reproduce asexually

• Leave snails and form cysts on grass which is eaten by the sheep and start over

Prevention

• Spray and kill the snails

Chinese liver fluke

• Infest the liver of humans

Life cycle

• Adults live in the human liver, mate, eggs leave with feces which is used to fertilize fields

• Flood irrigation washes them into rivers, hatch into larvae which enter snails, reproduce asexually

• Leave snails and enter fish which are eaten raw by humans and start over

Prevention

• Cook the fish• Use other fertilizers• Other irrigation methods