All Cnidaria are armed with stinging cells called nematocysts.
There are four major groups of Cnidaria: Anthozoa, Cubozoa, Hydrozoa, and
Scyphozoa.
They have radial symmetry.
At some point in their lives they develop a medusa and a polyp stage.
-
Medusa- a free-swimming bell,
shaped stage, with tentacles extending below the bell.
-
Polyp- Vase shaped, sedentary
stage of Cnidarian life cycle.
They
have a gastrovascular cavity that serves as a mouth for eating prey and as an
anus.
They are free-swimming and floating at different stages in their life.
Below is a Portuguese man-of-war