Gabitan, John Paulo
Tero, Nariza L.
Valencia, Juliet D.
Zapanta, Schola Marie
• Radially symmetrical cnidarian body is
organized as a hollow sac with the mouth and
surrounding tentacles located at one end.
• Based on molecular data, some systematists
have proposed that cnidarians share a
common ancestor with the clade of bilateral
• Cnidarians have two body shapes: polyp and
• Polyp form, represented by hydra, typically
has dorsal mouth surrounded by tentacles.
• Medusa form, the mouth is located in the
lower concave or oral surface; the convex
upper surface is the aboral surface.
• Cnidarians get their name from specialized
cells called cnidocytes that contain stinging
• It is found mainly in epidermis especially on
• Cnidocytes contain stinging “thread capsule”
• Cnidarians use their tentacles to capture prey
and they push it into the mouth and it leads
to gastrovascular cavity, where digestion
• Mouth is the only opening into gastrovascular
cavity that serves for both ingestion of food
and expulsion of undigested material. Gas
exhange and excretion occur by diffusion.
• Cnidarians are diploblastic meaning thay
have 2 definite tissue layers.
• Ectoderm which give rise to outer (covering
of body) and endoderm gives rise to inner
gastrodermis, which lines the gastrovascular
cavity and functions in digestion.
• These thin layers are separated by a thick,
jellylike mesoglea, which is mainly
• Cnidarians have nerve cells that form nerve
nets connecting sensory cells in the body
wall to contractile cells and gland cells.
• Hydrostatic skeleton supports the body
and allows movement.
• Mainly marine but
some are freshwater
• Alternation of polyp
and medusa stages in
most species (polyp
form only in Hydra)
• Some form colonies
• “True” jellyfish
• Mainly marine
• Typically inhabit
coastal water, free
• Polyp stage is often
• Inhabit tropical and
• Have polyp stage
but medusa form
• Square shape when
viewed from above
• Actively hunt prey
• Complex eyes that
• Solitary or colonial
• No medusa stage
cavity divided by
increasing area for
• Coral reefs (Anthozoans) serves as a habitat
of fishes and this may also serve as a tourist
attraction to humans.
• They also provide a home for algae which
creates oxygen that we breathe. The coral
reefs are also important because the polyps,
algae, and animals in that habitat are a
major food source for other animals.