Phylum Cnidaria Anemones, Corals, Hydroids and Jellies

Phylum Cnidaria Three classes: Class Anthozoa Class Scyphozoa Anemones Corals Class Scyphozoa True jellies Class Hydrozoa Hydrozoans

Same body plan for all classes

Differences between Classes Some spend more time in the medusa or polyp form Can reproduce differently Can be colonial or solitary

Cnidaria Characteristics Symmetry: Radial Level of Organization: Tissue Two cell layers (epidermis and gastrodermis) around a jelly-like substance (mesoglea)

Feeding: Excretion: Suspension feeding Single opening (mouth/anus) into a gastrovascular cavity All are carnivores Have light sensing organs (ocelli) Excretion: Wastes diffuse out of the cells into the water

Defense / Predation: Stinging Cells All Cnidarians have stinging cells to protect themselves A nematocyst is triggered with a hair cell It ejects a harpoon or string with a toxin

Class Anthozoa Corals and anemones dominant polyp life stage

Anemones Solitary: Usually one large polyp Some can “swim” away if attacked Some have symbiotic relationships, e.g. with clownfish or shrimp

Corals Corals are colonial animals Hard Corals Many polyps live on the outside of a calcium carbonate skeleton

Soft Corals Many polyps live together but without the hard skeleton

Reproduction Both sexual and asexual reproduction Asexual reproduction budding or fission (splitting in two) Sexual reproduction Spawning Female eject eggs and males eject sperm into the water Timed to the phase of the moon!

Soft Corals

A hard coral close up

Hard Coral Table coral has a large flat top to take advantage of sunlight

Purple Stubby Coral Some grow in small finger-like projections

Staghorn Coral

Mushroom Coral

Brain Coral

Special relationships with algae Coral animals have a symbiotic relationship with a kind of algae called zooxanthellae Mutualistic relationship – they both benefit one another

Zooxanthellae Does photosynthesis and gives the coral food (90% of the coral’s food is from here!) Coral gives the zooxanthellae a stable home gives the zooxanthellae nutrients from its waste

Colourful corals! The algae are responsible for the beautiful colours we see

Coral bleaching Zooxanthellae are very sensitive to temperature change and pollution If the temperature becomes too high, they leave the coral This is coral bleaching. Without the zooxanthellae, the coral will die.

Where would you rather dive? Here…

Or here…?

Class Scyphozoa Jellies Dominant medusa stage Some have both polyp and medusa stages

Coastal Jelly Life Cycle An ephyra larva

More images of the Jelly Life Cycle...

Powerful defenses Some jellies inject a very painful sting with their nematocysts Box jellies and sea wasps may be fatal

Class Hydrozoa Hydrozoans Colonial with specialized individuals to float, reproduce, defend or hunt. Some have both polyp and medusa stages Some have a skeleton of chitin

Portuguese Man O’ War specialized polyps to float and sting

Hydra lives in fresh water has only a polyp stage can reproduce by budding

Other Cnidarians Gorgonians like sea pens and sea whips are also in Phylum Cnidaria