Radiate animals
Phylum Cnidaria
 mostly marine w/some freshwater
 9000 sp.
 Class Anthozoa  Class Staurozoa –
 Class Scyphozoa –
 Class Cubozoa –
 Class Hydrozoa –
General characteristics
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Body organization
 2 germ layers give rise to two tissue layers:
 ectoderm 
 endoderm 
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in btwn two above layers.
 many cnidocytes have nematocysts - a tube-like capsule with coiled thread
Cnidocyte function
 they evert when projection called
stimulated.
 mechanism for release:
(not in anthozoans) is
 nematocyst may have barbs or spines w/toxins or sticky secretions used for
attachment
Body forms:
1) polyp – stationary
 asexual & sexual reproduction
 cylindrical body (column) with tentacles used for gathering food
 solitary or colonial
 Ex: sea anemones, corals, hydroids
2) medusa – mobile
 dioecious.
 upside-down cup w/tentacles
 more mesoglea
 Ex: jellyfish
Alternating generations - hydroids, jellyfish
Feeding
 gastrovascular cavity –
 carnivorous diet, mostly small crustaceans, or fish for anthozoans
 capture prey w/nematocysts, tentacles bring food into GV cavity thru mouth
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digestion inside GV cavity. gland cells produce enzymes
& mucus
 gastrodermis cells phagocytize partially-digested food Ecological, economic, or medical significance
 Corals  some cnidarians used for food by other animals, but not of econ. importance
to humans
 symbiotic relationships –
 cnidarians provide protection for animals that they live on or near,
 algae live in tissues in some hydra & corals
Phylum Ctenophora
 comb jellies, sea walnuts
 90 sp
 marine, esp. warm waters
 sim. to cnidarians - diploblastic, biradial symmetry, mesoglea, GV cavity,
nerve net
Distinguishing characteristics
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(adhesive cells)
8 rows of
. used in locomotion, most are free-swimming
GV cavity is branched w/some dead ends, has anal pore
statocysts used for equilibrium & orientation
monoecious