Cnidarians

Phylum Cnidarians

 
Characteristics-
	Produce nematocysts (a barbed organelle)- to harm organisms
	Cnidocyte – when trigger is stimulated the nematocyte is released 
		Contains: 
			trigger- to “feel” stimulus to release nematocyte
			body sac- holds nematocyte
	Nerve net- whole body reacts to any stimulation
		Lacks central nervous system (brain)
	Hydrostatic Skeleton- (water trapped) water moves in the mouth and is trapped by the mouth muscle (sphincter) 
	and the water pressure supports the body
	2 Layered body wall
		Epidermis- skin layer 
		Mesoglea- glue layer 
	Undifferentiated cells interstitial (means in and among) cells can become different types of cells
	Predators that are stationary
	Pharynx- “throat” opening that leads to gastrovascular cavity
	Incomplete digestive systems (inefficient)- has only one opening (mouth)

Life Cycle-

Asexual Reproduction- Forming buds by mitosis, that become new polyps
Sexual Reproduction- (Diecious- male and female medusa) 
	Egg is fertilized by sperm
	Zygote is created 
	Develop into blastula
	Develop into plantula larva
	Develop into polyps
	Polyps can branch – they have many feeding heads because they are one time use 
Only
Reproductive polyps- gonangium – produces medusae
Medusae swim, cluster and relese sperm and eggs into water to be fertilized

Four Classes

Class Anthozoa (anemones, corals, etc.)
Class Hydrozoa (Portuguese Man o' War, Obelia, etc.) Hydra, Physalia
Class Scyphozoa (jellyfish) Aurelia
Class Cubozoa (box jellies)



Class Scyphozoa (jellyfish) Aurelia
	Reproduce with medusa
	Modified polyp on gonangia
	Medusa- protein-atious (not cellular) mesoglea that makes jelly fish “jelly”
 	Aurelia- common Atlantic jellyfish
	Chrysaora- Chesapeake Bay jellyfish\
	Sea nettle
 

Class Hydrozoa
	Gonads on side of body
	Asexual budding is common
	Obelia- has a typical life cycle of a Cnidarian
	Portuguese Man o' War- toxic venom- a colony of polyps
 	Hydra – only polyp – no medusa


Class Anthozoa 
	Only polyps no medusa 
	Form gonads inside polyps
	Gametes relased through mouth
	Form plantula larva
Sea amemomies – Metridium
	Coral – produce CaCO3 skeleton