Transcript Phylum Cnidaria

Phylum: Cnidaria
(Coelenterata, Ctenophora)
Jellyfish, Sea Anemones,
Hydriods and Corals
Things that Sting!!!!
General Characteristics
• All Cnidarians contain stinging cells called
nematocysts which they use to paralyze
and trap prey so that they can move them
to their mouth area for digestion.
• Cnidarians have two body stages:
Medusa: free moving planktonic
Polyp: non moving sessile
Class: ANTHROZOA
Corals & Anemones
Corals are invertebrates that are in
symbiosis with an algae - that means they
exchange nutrients or other services with
one another in order for both to survive
better. They have an alternation of
generations during their life cycle (this
cycle alternates from a medusa to a polyp
stage). However, the class anthozoa's
medusa stage is short and once they fix
themselves in one place, they become
sessile.
Corals come in all shapes and sizes--some
are reef-builders while others are non reefbuilders:
Reef builders build high structures
composed of living and non-living
materials. The living materials are most
often sponges, algae, and the corals
themselves. The non-living materials are
most often the discarded shells of dead
bivalves (clams, mussels, etc.) and other
CaCO3 materials. Coral reefs grow about
a meter every one thousand years.
Non reef-builders usually inhabit the bottom
of more shallow areas of the ocean. They
do not build high structures.
A sea anemone will usually attach itself to
rocks or coral. They have a central mouth
which is surrounded by tentacles with
nematocysts, paralyzing and entangle
small marine animals.
Sea anemones primarily reproduce
sexually: They exist only in the polyp stage
and obtain their food by filter feeding.
Class: HYDROZOA
Hydroids & Siphonophores
The animals of the class hydrozoa have
both a polyp and medusa stage.
Siphonophores are a type of hydrozoan
with a float for buoyancy. Probably the
most famous of these is the species
physalia, the Portugese-man-of-war,
which is a type of colonial siphonophore.
Portugese-man-of-war
Class: SCHYPHOZOA
Jellyfish
Jellyfish are cnidarians which lack the
polyp stage of the life cycle.
Therefore, they are always in the
medusa stage. They are considered
plankton because they cannot swim
on their own--they are dependent
upon the current to take them places