You are viewing this Phylum as classified by:  IUCN threat
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Cnidarians are a diverse group of aquatic animals. More than
9,000 species are part of the Phylum Cnidaria, and all species
are aquatic. Cnidarians are widespread in marine habitats and
less common in fresh water.  This interesting group of
invertebrates includes many charismatic organisms such as
hydras, sea fans, jellyfishes, sea anemones, corals, and the
Portuguese man-of-war. Cnidarians all have some type of
specialized stinging cell organelle.  Cnidarians' bodies
typically take one of two forms: the polyp or the medusa. While
the polyp form is adapted for a sedentary or sessile lifestyle,
the medusa form is adapted for floating or free-swimming. Sea
anemones and corals (class Anthoza) are all polyps. True
jellyfishes (class Scyphozoa) are all medusae, though some have
a polyp larval stage. Notably, some hydroids (class Hydrozoa)
alternate between polyp and medusa forms throughout their lives.