c. Platyhelminthes Jessica Calahorra 9B
Feb 24, 2016
c. PlatyhelminthesJessica Calahorra 9B
Phylum Platyhelminthes Turbellaria Monogenea Trematoda Cestoda
Monogenea
TrematodaCestoda
Turbellaria
Reason for Name The name Platyhelminthes comes from
two Greek words. Platy = flat Helminthes = worm
Species Currently Existing There are 20,000 species. They are divided into the four sub-
phylas.
Characteristics Nothing is known from their evolutionary history because
they have very soft bodies which do not preserve well as fossils.
No internal cavity. Some species occur in all major habitats. Parasitic species. Sac Body Plan: it has one opening which functions as a
mouth and an anus. 3 germ layers- ectoderm (outermost layer), mesoderm
(middle layer) and endoderm (inner most layer-digestive track)
Bilateral Symmetry They are Hermaphrodites It has a mouth but no anus. Asexual + Sexual Reproduction
First Fossil The first fossil appeared on Earth was
40 million years ago. It was a Turbellarian fossil.
Life Cycle (Trematoda)
They are mainly parasites of vertebrates. The males are shorter and fatter than the females, and have a ventral
groove along their body, into which the female can fit. The fertilized eggs break into the host’s bladder and pass out with the
urine into the soil. The worm hatches and enters the body of a snail. In the snail’s body cavity, it grows into a large sac. It then hatches into a
greater worm stage called the redia. The redia has a mouth and an intestine and migrates to the snail’s
digestive organ. The redia develops into a tiny version of the adult, which drops out of the
snail and goes into the water where it might enter a human body through the mouth or the skin.
Life Expectancy: 100-200 years
Digestive System It is a combination of digestive and excretion system. Its a blind system since there is only one opening. The food enters the mouth, which goes to the
endodermal layer wich takes place the absorbtion and the digestion of the food.
It is digested in the gastrovascular cavity. Any non-digestable food is spit out through the mouth
(vomit). Platyhelminthes normally eat soft coral, bryozoan and
other invertebrates.
Circulatory and Respiration System
Platyhelminthes lack circulatory and respiration organs, that’s why their bodies are so flat.
The flat body allows the movement of oxygen and nutrients to reach all the parts of the body.
Its a diffusion process. Carbon dioxide leaves the body through this
process. Respiration occurs through diffusion.
Sensory System The sensory organs are detected near
the head. They detect sight, touch, movement… It also senses food.