|This phylum's 'place'
relative to other phyla:
|Selected taxa within this taxon:
Cnidarians are a diverse group of typically marine organisms with a fairly simple body plan: ~10,000 living species described.
Relatively early emergence in fossil record
|Possible link to Ediacarian fauna||Paleozoic corals though different coral taxa than modern reefs are composed.||Soft-bodied cnidarians also know from Cambrian|
A flotilla of giant jellyfish marooned on a beach
Similar to other phyla that are
without bilateral symmetry and without three tissue
layers. Does sharing of
primitive characteristics indicate that these phyla are more
closely related to each other than to triploblastic, bilateral
phyla? If diploblasts are not a monophyletic group, is
this evidence that ancestral triploblasts were diploblasts?
(a body plan song)
How can jellyfish continue to
sting even after they are dead?
Sensory organs: Statocysts and ocelli.
|"A" Portuguese man-of-war is composed of
various types of polyps for feeding,
reproduction and bouyancy.
What is the advantage of this
alternation of generations? Why is sexual reproduction
associated with the medusa stage?
Do all cnidarians alternate
(metamorphosize) from one form to the other (both medusal and
polyp stages)? See below.
Example of the class:
The true jellyfish
Example of the class: Aurelia aurita
Small class in size and diversity and recently considered in a different order than Scyphozoa.
- approximately cuboid in shape with 4 complex eyes
- margin of the bell is frequently turned inward
There is presently debate on whether Hydrozoa or Anthozoa is the most primitive cnidarians: