Phylum CnidariaSEA JELLIES, HYDRA, CORAL COLONIES, SEA ANEMONES

Sea Jellies

Hydra

Coral Colonies

Brain coral

Sea Anemones

Sea Pens

Sea Fans

Phylum CnidariaOver 10,000 known speciesMicroscopic – 4 meter diameterSolitary or colonial

Phylum Cnidaria CharacteristicsBody Type: Radial SymmetryBody Organization: Diploblastic

Two germ layers (endoderm and ectoderm)

Mesoglea: Jelly layer between endo and ectoderm, not a true tissue layer

Body Cavity: Acoelomate

Phylum Cnidaria CharacteristicsBody Plan: Many have both body plans

in their life cyclePolyp – Attached to substrate, sessileMedusa – Free swimming

Phylum Cnidaria Characteristics

Ecological RolesFood sourceHome/shelterSymbiosis with algae/protistsWave break to protect shore lines

Phylum Cnidaria CharacteristicsDigestive System

Sac body: Single opening (mouth/anus)

Central gastrovascular cavity

Specialized stinging cells (cnidocytes) contain coiled fibre (nematocyst)trap or paralyze prey

This Phylum has nematocysts for feeding & defense:

Phylum Cnidaria CharacteristicsReproduction

SexualMostly dioecious (sexes separate)External fertilization Egg and sperm form planula larva

AsexualBudding

Phylum Cnidaria CharacteristicsNervous System

Display coordinated movementNerve net over entire bodySensory cells concentrated near mouth

detect light, chemicals, or touch.

Phylum Cnidaria CharacteristicsCirculation & Respiration: Open

systemBody contractions create currents to

circulate materials through GV cavity.Diffusion moves substances in and

out of cellsExcretion: Solid wastes expelled

through mouth opening

Classification of CnidariansClass Schyphozoa “Jelly Fish”

Majority of life cycle as free swimming medusa form

Ex. Aurelia aurita (Moon Jelly)

Classification of CnidariansClass Anthozoa Anemones, Corals

No medusa stage.Polyps solitary or colonialAll marineEx. Anthoplera elegantissima

(Aggregating Anemone)

CoralsCorals are colonies of polyps

contained in a hard calcium carbonate skeleton

Classification of CnidariansClass Hydrozoa Hydroids

Alternation of generations between polyp and medusa

Colonial Polyps - PolymorphicEx. Obelia sp. / Physalia physalis

Man of war jellyfish