Welcome

Cnidarians include hydroids, sea anemones, corals and jellies. This group is more advanced than the sponges, and has a tissue level of construction. Only two tissues layers are present: ectoderm and endoderm. A jelly layer called mesoglea (especially noticeable in jelly fish) is found between the epidermis and gastrodermis.

Basic jelllyfish structure.

Cnidarians have a true mouth and digestive cavity, but no anus. What goes in, also must come out the same opening! Tentacles surround the mouth opening to trap prey. These animals are usually carnivores, eating crustaceans, molluscs and small fish. Many corals and anemones contain symbiotic zooxanthellae (a type of cyanobacteria). The zooxanthellae provide oxygen and some nutrition and are important for coral reef formation.

Cnidarians are made unique by the present of stinging organs called nematocysts. Nematocysts are poisonous, sticky, or barbed filaments released from special cnidocyte cells. Nematocyst release is triggered by chemical or tactile stimulation and they are used for defense, food collection and some locomotion. Nematocysts are responsible for the sticky feeling of anemones and the poisonous sting of some jellies.

Anthopleura elegantissima
(Aggregating Anemone)
Description: Green tentacles with pink/purple tips. May be solitary or in colonies.
Range: Alaska to Baja, California
Habitat: Rocks above low tide line and in tidepools in exposed areas.
Cool Fact: Use asexual reproduction to produce large colonies of clones! (can also reproduce sexually)

Anthopleura xanthogrammica
(Giant Green Anemone)
Description: disk and tentacles are green or blue-green; often covered with pieces of shell

Range: Alaska to Panama
Habitat: Exposed, rocky shores; intertidal to 15m and deeper.
Cool Fact: Green colour comes from symbiotic cyanobacteria. Can live for 30 years!

see also: Strawberry Anenome, and Anthopleura and Metridium pages!

to Intertidal Field Guide directory