• Coelom:
• Fluid-filled body
cavity lined by
cells from the
mesoderm
•In mammals it
forms the
peritoneal, pleural
and pericardial
cavities
Acoelomate
Pseudocoelomate
Coelomate
Phylum Platyhelminthes:
Say What???
Flat Worms: Planarians, Tapeworms, & Flukes
TAPEWORMS!!!
Characteristics of Flatworms
• Flatworms are the simplest of the worm
groups; 20,000 species
• SIMPLEST ANIMALS W/ ORGANS:
ganglia, eye spots, testes, ovaries,
nephridiopores
• They are found in many places and can be
free living or parasitic.
• A flatworm can be microscopic or many
feet long and is generally very thin.
Characteristics of Flatworms
• Show cephalization: “sensory organs in
front of head to sense food, danger,
mates”
• One of the best-known flatworms is the
tapeworm. The tapeworm can get into a
person's digestive tract and grow to
enormous lengths.
• Flatworms are found in marine and fresh
water.
Body Cavity
• Acoelomate: lack an internal body cavity
Muscular-Skeletal System
• A flatworm has no skeleton. It has tiny
bristles called cilia that help it move as
well as two layers of muscles under its
skin. It has three cell layers called the
endoderm, the mesoderm and the
ectoderm.
Digestion
• Mouth/Anus: It takes food in and gets rid
of wastes through the same opening
(pharynx).
• A flatworm has a gastrovascular cavity
(highly branched) with one opening.
• It eats small worms, insects and
microscopic matter.
Digestion (cont.)
Nervous System
• A flatworm has a very simple nervous
system with two nerve cords running down
either side.
• It has two simple brains called ganglia,
which are simple bundles of nerves.
• It has two eyespots that help it sense
light.
Nervous System (cont.)
Circulation
• NONE!!
Respiration
• Oxygen/carbon dioxide pass through
worm’s body by diffusion
Reproduction
• Sexually: hermaphrodites: simultaneous
fertilization
• Asexually: A flatworm reproduces by
splitting in two. When a flatworm is split up
it immediately forms a new flatworm.
• Flatworm Regeneration video
Planaria
Excretion
• A flatworm gets rid of wastes through the
same opening it takes in food. Also, have
flame cells (w/cilia) to get rid of excess
water.
Symmetry
• A flatworm has bilateral symmetry.
Other types of Flatworms
Tapeworms
Other types of Flatworms
Flukes
Fluke life cycle