Updated by: Arabinda Naik
Phylum Phylum Platyhelminthes include flatworms. The group include the first simplest triploblastic group of animals. It includes about 12,000 species of animals. They have leaf like or ribbon like body.
General Features
Habit and Habitat Majority of forms are parasitic and free-living forms (planarians). Hooks and suckers are present in parasitic forms.
Symmetry The body is bilaterally symmetrical with definite orientation like anterior and posterior end.
Cephalisation Primitive cephalisation is present in free- living flatworms.
Germ Layers They are triploblastic.
Body Cavity They are acoelomate. The space between the body wall and body organ is filled by characteristic connective tissue called parenchyme or mesenchyme.
Body Organisation They show organ system grade of organisation.
Digestive System It is simple and incomplete with only one opening called mouth. The anus is absent.
Respiration It occurs through general body surface.
Excretory System It consists of peculiar flame cells that can help in osmoregulation and excretion.
Circulatory and skeletal systems are absent in Platyhelminthes.
Nervous system: It is ladder like and consist of brain and two main longitudinal nerve cords joined at interval.
Reproduction: Flatworms are hermaphrodite, monoecious or bisexual, having both male and female reproductive system. Fertilization includes one or more larval stages. Some also have regenerate. Planaria, Taenia