Page 3 - 2.Lesson Notes-Animalia 1

• Sessile forms are called Polyps and free-living forms are called Medusa.
• Cells are organized into tissues (tissue grade of the organization).
• Animals are diploblastic, outer ectoderm and inner endoderm. Mesogloea
separates these two layers.
• The body has a single opening called hypostome (mouth)surrounded by
sensory tentacles.
• Body cavity (coelom) acts as gastrovascular cavity i.e. coelenteron.

• special types of cells called Nematocysts are present for capturing and
paralyzing pray, present in tentacles.

• Examples: Hydra, Jellyfish, Corals, Obelia, Sea-anemone.

Platyhelminthes

• This phylum consists of the organisms are bilaterally symmetrical, triploblastic
and flattened.
• Organ- system grade of the organization is seen.

• Animals are triploblastic with outer ectoderm, middle mesoderm and inner
endoderm.
• Acoelomate i.e No body cavity.

• The digestive system is incomplete or absent.
• Mostly parasites, few are free living.
• Examples: Liver fluke, Tapeworm.