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Cnidaria General Characteristics The name Cnidaria comes from the Greek word "cnidos," which means stinging nettle An exclusively aquatic phylum Tissue level organization They have stinging cells called nematocysts Generally, their bodies are two cell layers thick Radial symmetry; Little specialization; Pseudocoelomate Extracellular digestion Hydrostatic skeleton Both asexual and sexual reproduction External fertilization One opening, the mouth http://fotokudra.lt/files/I261542.jpg Class Hydrozoa (Hydroids) Hydra http://kentsimmons.uwinnipeg.ca/1 6cm05/16labman05/lb5pg3_files/h ydra3.jpg Obelia http://www.wallawalla.edu/academics/departments/b iology/rosario/inverts/Cnidaria/ClassHydrozoa/HydroidPolyps/Obelia_dichotoma.html Goneonemus http://www.biology.iastate.edu/Courses /211L/Cnidar/%20CnidINDX.htm Class Scyphozoa (Jellyfish) Aurelia http://seanet.stanford.edu/HydroScyphozoa/aurelia_lab580.jpg Class Anthozoa (Corals & Sea Anemone) Sea Anemone http://www.valdosta.edu/~jlgoble/Sea%20Anemone%20Diadumene%20Dia%2030c m%201.JPG Class Cubomedusa (Box Jellyfish) Box Jelly http://thestashbox.files.wordpress.com/2009/02/226boxjellyfish1.jpg Body Plan Tissue level of organization Outer covering (epidermis), inner gasterodermis, non-cellular mesoglea between the two; Diploblastic, body and tentacles consists of two cell layers Possess stinging structures, nematocysts, housed in cells called cnidocytes; Single body opening, the mouth Radial symmetry Two body forms Polyp: cylindrical with tentacles at one end; Sessile (non-motile) but some capable of locomotion; mouth points upward; EX: The Hydra Medusa: Free swimming; Bell shaped; Swim by undulations of their bell; Thicker mesoglea mouth-side down; EX: The Jellyfish Some cnidarians exist only in polypoid or medusoid form, others alternate between the two Both diploid so not true alternation of generations Body Plan cont. http://biology.unm.edu/ccouncil/Biology_203/Images/SimpleAnimals/cnidariaDiagram.jpeg Carnivorous or filter feeders Medusa do not hunt for prey, use “sit-and-trap” method Uses cnidae and toxins to stun and kill prey Sessile ployps depend on organisms that come in contact with tentacles http://www.nick.com/multimedia/binits08 games/spongebob-jellyfishin-game.png Feeding Tentacles have stinging cells (cnidocytes) that contain small harpoons called nematocysts Harpoon propelled by osmotic pressure, spears prey and draws it back to hydra Both have a ring of tentacles around the mouth Extracellular digestion; gut cavity for digestion, lining cells engulf food by phagocytosis Enzymes secreted from the gastrodermis break down the food http://www.arcodiv.org/cnidarians.html Respiration Contains no respiratory system This image depicts the internal structure of a jellyfish (a Medusae cnidaria). Because the great majority of cells are directly in contact with the ocean water, a complicated respiratory system is not needed. http://www.arcodiv.org/cnidarians.html Circulation No circulatory system (blood vessels) Majority of cells come in direct contact of seawater Have gastrovascular cavity; inner cells exposed to water Only two cell layers thick, all cells exposed to water for nutrient and gas exchange http://www.connecticutvalleybiological.com/images/vc1336v.jpg Excretion Contains no excretory organs Gastrovascular cavity serves for gas exchange and digestion Gas exchange takes place directly across the surface of their body and waste is released either through their gastrovascular cavity or by diffusion through their skin No anus Excretes through mouth, only opening http://www.arcodiv.org/cnidarians.html Response Simple net like nervous system Coordinates contraction of muscles; Little central control http://www.arcodiv.org/cnidarians.html http://www.aboutmyplanet.com/files/2008/12/800pxJellyfish_in_the_Montery_Bay_Aquarium-resized.jpg Movement Polyp Sits on basal disk, used to glide around with help of mucus secretions Some can somersault, bending over and attaching itself to substrate by its tentacles and looping over to new location If polyp detaches itself from substrate, it can float to surface Medusae Outer layer, epithelium, contains specialized epitheliomuscular cells, each can contract individually These cells form muscular rings around the bell shape of the jellyfish; allows the animal to propel through water Reproduction Polyps reproduce asexually (budding and fragmentation) Medusae reproduce sexually Fertilization external Alternation between medusa, sexually reproductive stage, and polyp, the asexual stage Class Anthozoa has no medusa stage Medusae has a distinct larval stage which is planktonic; called planulae; multicellular, pear-shaped, entirely ciliated Jellyfish have separate male and females Medusae stage is dominant Some exhibit the medusa form throughout their life while others first pass through other phases before maturing into the medusa form Reproduction http://universe-review.ca/I10-82-cnidaria.jpg Works Cited "Introduction to Cnidaria." UCMP - University of California Museum of Paleontology. Web. 15 Apr. 2010. <http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html>. "Cnidarians." W. Fielding Rubel School of Business: Bellarmine University. Web. 16 Apr. 2010. <http://cas.bellarmine.edu/tietjen/images/cnidarians.htm>. "The Anemones, Corals and Jellyfish (Phylum Cnidaria)." The Earth Life Web. Web. 19 Apr. 2010. <http://www.earthlife.net/inverts/cnidaria.html>. Klappenbach, Laura. "Diet - Cnidarian Diet and Eating Habits." Animals Wildlife - Animal Facts, Animal Pictures, Habitat Facts, Evolution and Zoology. Web. 20 Apr. 2010. <http://animals.about.com/od/cnidarians/ss/cnidarians_6.htm>. "The Noncoelomate Animals." Biology. Sixth ed. Boston: McGraw Hill, 2002. 886-89. Print. Works Cited (Pictures) "Multi-cell Organisms." A Review of the Universe. Web. 16 Apr. 2010. <http://universe-review.ca/F10multicell.htm#Index>. "Simple Animals." Web. 19 Apr. 2010. <http://biology.unm.edu/ccouncil/Biology_203/Summaries/SimpleAnimals.htm>. "New Page 1." Virtual Microscope Home Page. Web. 19 Apr. 2010. <http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb5pg3.htm>. "Obelia Dichotoma." WWU: On Campus. Web. 19 Apr. 2010. <http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Cnidaria/ClassHydrozoa/HydroidPolyps/Obelia_dichotoma.html>. "Gonionemus." Biology Program at ISU. Web. 19 Apr. 2010. <http://www.biology.iastate.edu/Courses/211L/Cnidar/%20CnidINDX.htm>. "Hydrozoa & Scyphozoa." SeaNet. Web. 19 Apr. 2010. <http://seanet.stanford.edu/HydroScyphozoa/index.html>. "Search Results | SpongeBob.com." SpongeBob.com | SpongeBob SquarePants Episodes, Games, & Pictures. Web. 20 Apr. 2010. <http://spongebob.nick.com/search/game/spongebob%20games/0>. "Anemone." Valdosta State University. Web. 19 Apr. 2010. <http://www.valdosta.edu/~jlgoble/topic.html>. "Foto KÅ«dra - Fotografija - Cnidaria Scyphozoa II." FotoKÅ«dra - Fotografija | KÅ«ryba | Bendravimas. Web. 20 Apr. 2010. <http://fotokudra.lt/img.php?img=182032&nav=cat&page=156>. "Jellyfish Take Over Ocean: A Dangerous Warning Sign." Go Green. Web. 20 Apr. 2010. <http://www.aboutmyplanet.com/green-news/jellyfish-ocean/>. Hopcroft, Russ. "Cnidarians - Jellyfish and Kin." Arctic Ocean Diversity. Census of Marine Life, 4 Jan. 2008. Web. 20 Apr. 2010. <http://www.arcodiv.org/cnidarians.html>