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.