Biology 11Kingdom Animalia:Phylum Platyhelminthes:The Flatworms

Phylum Platyhelminthes Objectives

• Advances over Cnidarians• Body plan (systems and structures)• 3 classes and example animals• Parasitic worms (enter, live, hosts, effects)

The Acoelomates

The acoelomates advanced animal evolution in two significant ways:

1. Bilateral symmetry2. TriploblasticAre still primitive because lack a body cavity

Phylum Platyhelminthes

The FlatwormsCharacteristics and Advances1. Still have incomplete digestive system

with a gastrovascular cavity (just like Cnidarians) but…

2. They are the first phylum with an excretory system made of “flame cells” and pores (so mouth is no longer anus as well!)

Phylum Platyhelminthes

3. Have a “Nerve Ladder” type of nervous system

4. Reproduce mostly sexually but have excellent powers of regeneration which can be a form of asexual reproduction

5. Cephalization begins with a “brain” and sense organs appearing anteriorly in a head

Phylum Platyhelminthes

Class Turbellaria• Includes the

Planaria a fresh water flatworm• Also includes many

marine varieties

Planaria sp.

Phylum Platyhelminthes

Class Trematoda• Includes the parasitic

flukes • Include liver, blood, lung,

heart, and intestinal flukes•Many have intermediate

hosts like this liver fluke (i.e. sheep, cow, fish etc)

Fasciola hepatica

Fasciola hepatica (Liver Fluke)

Fasciola hepatica Life Cycle

Phylum PlatyhelminthesClass Cestoidea: the tapeworms• Classical endoparasite appears

degenerative but actually highly evolved to its habitat• Human tapeworms can grow up to 20 m

long!

Tape worm Anatomy

Tape worm Life Cycle