Flatworms are soft, flattened worms that have tissues and
internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry and
cephalization.
Tubellarians are free-living marine or freshwater flatworms.
Flukes are parasitic
flatworms that usually infect the
internal organs of their hosts
Tapeworms are long, flat parasitic worms that are adapted to
life inside the intestine of their hosts.
Reproduction in Platyhelminthes:
Most free-living flatworms are hermaphrodite that reproduce
sexually. A hermaphrodite is an individual that has both male and female
reproductive organs. During sexual reproduction, two worms join in a pair. The
worms in the pair deliver sperm to each other. The eggs are laid in clusters
and hatch within a few weeks. Asexual
reproduction is common in free-living flatworms. It takes place by fission, in
which and each half grows new parts to become a complete organism. In some species,
a worm simply “falls to pieces”, and each pieces grows into a new worm.
Parasitic flatworms often have complex life cycles that involve both sexual and
asexual reproduction.
Respiration in Platyhelminthes:
Because their bodies are so flat and thin,
many flatworms do not need a circulatory system to transport materials.
Instead, flatworms rely on diffusion to transport oxygen and nutrients to their
internal tissues, and to remove carbon dioxide and other wastes from their
bodies. Flatworms have no gills or other respiratory organs, and no heart,
blood vessels, or blood.
