Phylum Cnidaria= Greek for “nettle”
 Next evolutionary jump
 Radial symmetry
 Tissue organization
 No organs
 The “stingers”
 10,000 species, mostly
marine
 Ex: jellyfish, corals, sea
anemones, sea pansies,
sea fans, gorgonians
Radial Symmetry & anatomy
 Radial symmetry = similar parts of body are arranged and
repeated around a central axis.
 Ex: if animal cut like a pizza, all slices would be similar
 NO head, front, back
 Instead Oral Surface & Aboral Surface
 Oral Surface
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Central mouth surrounded by tentacles
Brings in food particles
Mouth opens into a gut (only 1 opening)
Used for ingestion and waste expelling
Gut cavity = “stomach”
 Aboral Surface-other end
Cnidarian Body Plan
Polyp
Medusa
 Anchored to bottom
 Free-floating
 Mouth upwards
 Mouth downwards
Some life history includes both, others are either polyp or medusa
Phylum Cnidaria
Nematocysts
 stinging structures for prey
capture
 Contained in cnidocytes,
specialized cells.
 Found on tentacles
 Harpoon filled capsules
 Fire when touched
 Nematocysts Firing
Feeding and Digestion
 Cnidarians are carnivores
 Can eat large prey
 Extracellular digestion
 Begins break down of food outside of gut cells
 Intracellular digestion
 Break down of food and uptake of nutrients is completed inside
cells of the gastrodermis
Phylum Cnidaria: 4 classes
 1) Hydrozoa
 2) Scyphozoans
 3) Cubozoa
 4) Anthozoans
Class Hydrozoa
Garveia annulata
Tubularia marina
Class Hydrozoa
Hydractina milleri
Aglaophenia
latirostris
Class Hydrozoa
Velella
velella
Hydrozoa:
 Feathery or bushy colonies of tiny polyps attached to
pilings, shells, seaweeds, and other surfaces
 Polyps may be specialized for feeding, defense, or
reproduction
Hyrodozoan life cycle
Obelia dichotoma
polyp and medusa
Class Scyphozoa
Haliclystus
auricula
Aurelia
aurita
Class Scyphozoa
Chrysaora
melanaster
Scyphozoa
 Larger jellyfish
 Large medusa dominates life cycle
 Bell reach diameter of 2 m (6.6 ft)
 Bell diameter-deep water species is 3 m (10 ft)
 Swim with rhythmic contractions of bell but easily
carried by currents
 Some species stings range from a rash to fatalities
 Cubomedusae once classified as scyphozoa now own
class Cubozoa. Ex: Sea wasp= Box-jellyfish
Class Anthozoa
 Most Cnidarian species are Anthozoan
 Ex: Corals, anemones, sea fans, sea pansies
 Only polyp stage
 Corals ---calcium carbonate skeletons forming coral
reefs
Class Anthozoa
Anthopleura
xanthogrammica
Metridium senile
Class Anthozoa
Anthopleura
elegantissima
Class Anthozoa
Tealia
lofotensis
Epiactis
prolifera
Symbiotic Relationship
 Clownfish eat
undigested anemone
prey which could rot and
cause disease
 Anemones eat fecal
waste of fish
 Clownfish not affected
by nematocysts toxins
 Anemones provide safe
shelter for fish
Corals, Anthozoa
 Hard calcium carbonate
skeleton
 Cold and warm waters
 In warm waters, form
coral reefs
 Symbiotic zooxanthelle
(single celled,
photosynthetic algae)
Class Anthozoa, corals
Phylum Cnidaria: 4 classes
 1) Hydrozoa
 2) Scyphozoans
 3) Cubozoa
 4) Anthozoans
Phylum Ctenophore
 The comb jellies
 Less than 100 species
 Radial symmetry
 8 rows of ciliary combs,
that beat in waves