Phyla Cnidaria and Ctenophora: An Overview
Cnidaria
•	Diploblastic (blastula has endo- and ectoderm)
•	Tissue-level organization
•	True mouth (a.k.a. anus)
•	“Naked” nerve nets- no CNS
•	Unique presence of Nematocysts
•	Planktonic or sessile 
Ctenophora
(Comb jellies) 
•	Weak swimmers- planktonic or benthic
•	Statocyst present- organ determines orientation, contains statoliths and four groups of fused cilia
•	Often source of nighttime multi-colored bioluminescence 

Radiata Side by Side
•	Jellyfish, anemones, corals 
•	Mainly carnivorous
•	Move by water propulsion
•	Exclusively aquatic, mostly marine
•	Tentacles unbranched, around mouths of polyps, margin of medusae
•	Tentacles hollow w/ nematocysts 

•	Comb Jellies
•	Carnivorous 
•	Move by ctenes (fused cilia)
•	Exclusively Aquatic, mostly marine
•	If present; two tentacles, branched and extensile
•	Tentacles solid w/ colloblasts
Cnidaria- Major Classes
Anthozoa 
(corals and 
anemones)
•	About 6500 species
•	No medusa stage
•	Some hermaphroditic 
•	Thrive best in presence
of symbionts-
(usually heterotrophic
dinomastigotes)

Hydrozoa
(hydras and man-of-war)
•	About 3100 species       
•	Most medusae with velum
•	Many with small
or absent medusa
•	Polyps usually bud daughter polyps
•	Medusae reproduce sexually

Scyphozoa
(“True” jellyfish)
•	200 species- all marine
•	Thick mesoglea
•	No vela
•	Alternation of generations
•	Medusae sexual, giving rise to polyps
•	Polyps sessile and asexual, giving rise to ephyra

Cubozoa
(Sea wasps)
•	One or more tentacles at each of the four corners of their medusae
•	Tropical and subtropical swimmers
•	Nasty stingers
•	Among most complex invertebrate eyes
•	Alternation of generations

When is a jellyfish like a honey bee?

     

         Nematocysts: More firearm                            	than syringe? 
•	Study sequenced mediterrean jellyfish, Rhopilema nomadica venom. 
•	Identifed unique mechanical process of venom translocation. 
•	Polypeptide lysis of cells 
•	Neurotoxic effects
•	Affect neurotransmitters
•	Striking similarity to Gila monster venom

Citations
Kozloff, E. Seashore Life of the Northern Pacific Coast. 1993. Seattle: University of 
	Washington Press.

Lotan, A., L. Fishman, and E. Zlotkin.  1996. Toxin compartmentation and delivery in the cnidaria: The nematocyst’s tubule as a multiheaded poisonous arrow. Comparative Physiology and Biochemistry. 275:444-451.

Margulis, L., and K. Schwartz.  1998.  Five Kingdoms: An illustrated guide to the phyla of life on Earth.  New York: Holt. 

University of California, Irvine. April 2, 2006. Cnidaria home page. 
	http://tolweb.org/Cnidaria/2461/1997.04.24 in The Tree of Life Web Project, 
	http://tolweb.org/ 

University of Ottawa. April 1, 2006. Cnidarian information page. http://biodidac.bio.uottawa.ca