Phylum Cnidaria

A Powerpoint Presentation by Sophia DiCamillo

andWill Guiteras

Characterization of Cnidaria ● Member of the clade Eumetazoa (true tissues)● Diversified into range of both sessile and

floating forms● These include:

○ Jellies○ Corals○ Hydras

● Simple, diploblastic bodies; radial symmetry ● Carnivorous● No brain, rather a nerve net

Gastrovascular Cavity ● Definition: A sack with a central digestive

compartment● A single opening to this cavity serves of dual

function of cavity and anus● Two types:

○ Sessile Polyp○ Floating Medusa

Gastrovascular Cavity (cont.)● Polyps: Cylindrical forms that adhere to the

substrate by the aboral end (opposite of mouth) of the body and extends their tentacles waiting for prey○ Example: Hydra○ Example: Sea anemone

● Medusa: Flattened mouth-down version of a polyp. Moves freely in the water by a combination of passive drifting and contractions of its bell-shaped body.○ Example: Jellyfish

● Some Cnidarians are just one, while others have both stages

Polyp vs Medusa

Cnidocyctes● Definition: Unique cells that function in

defense and the capture of prey ● Contain cnidae, capsule-like organelles that

are capable of everting and that give the phylum its name

● Cnidae called nematocysts are stinging capsules

● Nerves and tissues occur in simplest form● epidermis - outer layer● gastrodermis - inner layer

Cnidocytes Diagram

Class Hydrozoa● Most alternate between medusa and polyp

form● Hydras are unusual hydrozoans because

○ Only polyps○ Found in freshwater○ Reproduce by budding (asexual)

Class Scyphozoa ● Medusa is predominant stage of

scyphozoa ● Coastal scypozoans go through a

small polyp stage● Open ocean scyphozoans lack the

polyp stage○ Example: Jellyfish

Class Cubozoa● Name means "cube animals" ● Box-shaped medusa stage● Complex eyes● Generally live in tropical oceans ● They are equipped with highly toxic

cnidocytes ○ Example: Sea wasp, one of the deadliest organisms

on Earth ○ The amount of poison in a sea wasp can kill 60

people

Class Anthozoa● Means "flower animals"

○ Exmple: Sea anemone○ Example: Coral

● Occur exclusively as polyps● Corals secrete a hard external skeleton of

calcium carbonate; each polyp generation builds on the skeltal remains of earlier generations constructing rocks

● Coral reefs provide habitat for a wealth of other species

Cubazoa (box jelliies, sea wasps) All marine; No medusa stage; mostly

Sessile and Colonial