Outline • Classification • Characteristics • Reproduction • Description of the 4 classes • Current experimentation • Distribution • Fossil records
Classification Cnidarian - (Gr. Knide, nettle, + L. aria [pl. suffix] like or connected with) • Alternate phylum name is Coelenterate (Gr. Koilos, hollow, + enteron, gut, + L. ata [pl. suffix] • Consist of more than 9000 species • 4 classes
Aquatic (marine, some fresh water) Body structure (radial or biradial symmetry) Gastro vascular cavity Two layers (epidermis and gastrodermis) Nematocysts Two forms of cnidarians Polyp (attached) live in colonies Medusa (jellyfish) Free-swimming Characteristics of cnidarians
Class Scyphozoan(Gr. Skyphos, cup)“The true jellyfish,” can be characterized by a thick, jelly like bell made up of mesoglea and 95% to 96% water. Their entire body is covered with nematocysts, which packs a painful sting. Oral arms are their primary source for feeding and ingestion. Reproduction is sexual.
Class Hydrozoa(Gr. Hydra, water serpent, + zoon, animal)Mainly marine and live colonial. Consist of an epidermis, gastrodermis, and mesoglea. Hydras use a basal disc for movement and secrete mucous for assistance. The hydra relies on tentacles for feeding and digestion. They reproduce asexually (budding) and sexually, usually in Autumn.
Class Anthazoan(Gr. Anthos, flower, + zoon, animal).Only exist in the polyp form.Can live solitary as anemones or in colonies, such as corals. Possess a gastro vascular cavity subdivided by septa bearing nematocysts. Reproduction through separate sexes or asexually by budding, but commonly pedal laceration
Class Cubozoa(Gr. Kybos, a cube + zoon, animal).Size range up to 25 cm tall, but are usually 2 to 3 cm. The transverse of the bell appears square in these animals. On the corners of the bell are tentacles these help in moving and feeding. Reproduce by asexual budding.
Aequorin, composed of Calcium++activated photoprotein emits a blue-green light. This light is used by scientists to highlight genes for quicker studies. Current experimentationBioluminescence
Distribution Fungiid Coral from Indonesia
Distribution • Cnidarians generally occupy two major niches • Some use their cnidocysts to trap prey. Other cnidarians, such as anthozoans depend on zooxanthellae. These are, symbiotic dinoflagellates within their tissues. This is how they survive.
Distribution • These single-celled protists carry out photosynthesis within the animal's tissues, and pass on the carbon compounds they fix to their hosts; corals, therefore, are photosynthetic animals in a sense
Distribution • While not all corals are dependent on symbionts — some live at great depths where there is never light • colonial, reef-forming corals depend on these symbionts; therefore, reefs can only exist in shallow water. The white areas on the coral reef on the next slide show the reefs exposed at low tide. This loss of symbionts, called bleaching, is deadly to coral reefs.
Fossil Records • Cnidarian fossils date back to the time when animals first appear in the fossil record, the Vendian. Since then, the fossil record of cnidarians without mineralized skeletons is quite sparse, and restricted to unusual sites with excellent fossil preservation.
Fossil Records • Cnidarians which possessed hard skeletons, the corals, have left a significant legacy of their existence. While a few mineralized coral-like fossils have turned up in the Cambrian Period, identifiable corals began an evolutionary radiation in the Early Ordovician. These Paleozoic corals included taxa known as tabulate corals, rugose corals, and heliolitid corals. All these forms were wiped out at the end of the Permian Period, in a mass extinction event that claimed something like 95% of all marine invertebrate species (Foster, 1979)
Fossil Records • Scleractinian corals first appear in the Middle Triassic, about 15 milion years after the Permian extinction. They rapidly expanded into ecological niches once dominated by tabulate and rugose corals, and became the dominant hermatypic (reef-building) organisms in shallow tropical marine habitats. Because corals are sensitive to changes in light, temperature, water quality, and salinity, their fossils provide information that can be used to interpret climate and geography of past environments.
Scyphozoa • All scyphozoa are marine, though a few fresh water forms have occasionally been reported. • While many species live solitary lives, some like Aurelia may travel in shoals of hundreds to thousands of individuals stretching for dozens of kilometers.
Hydrozoans • Hydrozoans may date back to the Vendian (late Precambrian), but the fossil record of hydrozoans is scanty before the Cenozoic, starting about 65 million years ago. The oldest fossil milleporines and stylasterines — the "fire corals," so called from their stony growths that resemble those of true true corals — appeared in the Late Cretaceous and are moderately common as fossils in the Cenozoic
A rare fossil hydroid, Mississippidendrium from the Cretaceous of northeast Mississippi
Anthozoans • Anthozoans are exclusively marine, polypoid cnidarians. They occur from the intertidal zone to the depths of the trenches (to 6000 m). In excess of 6000 species currently exist (Hyman 1940), comprising about two-thirds of extant cnidarian species (Dunn 1982); some anthozoans, such as the scleractinian corals, have a rich fossil history (Wells and Hill 1956).
Cubozoans • A few probable cubozoans are known as fossils from the famous Mazon Creek locality (Pennsylvanian age) near Chicago, Illinois • Other fossils that may be cubozoans have been found in the JurassicSolnhofen Limestone of Bavaria, Germany
Dispersal • Cnidarians live in aquatic environments and inhabit all depths, from the sandy substrate up to the surface. They can be found from the Great Barrier Reef rising off the coast of northeastern Australia to the continental shelves of bone-chilling arctic oceans, and just about every saltwater marine habitat in between. (national zoo, 2008) • Some jellyfish are even found in freshwater lakes, such as the freshwater jellyfish (Craspedacusta sowerbyi), which haunts several lakes in New Zealand. Not to worry though, these jellyfish are harmless to humans and feed mainly on zooplankton (national zoo, 2008)
Figure 1a. Distribution map of 60 species of Chilean sea anemones according to the literature. The two species with doubtful classification and the species without location are not shown in the distribution map. p: type localities; D: type locality of synonymous species; : other collection sites; collection sites are connected by lines for greater clarity. NPZ: North Patagonian Zone, CPZ: Central Patagonian Zone, SPZ: South Patagonian Zone.
Works Cited • Conway Morris, S., 1993: The fossil record and early evolution of the Metazoa. --Nature, vol. 361, 21 January, pp. 219-225 • Daly, M, DG Fautin & VA Cappola (2003), Systematics of the Hexacorallia (Cnidaria: Anthozoa). Zool. J. Linn. Soc. 139: 419–437 • Fautin, Daphne G. and Romano, Sandra L. 1997. Cnidaria. Sea anemones, corals, jellyfish, sea pens, hydra. Version 24 April 1997. http://tolweb.org/Cnidaria/2461/1997.04.24 in The Tree of Life Web Project, http://tolweb.org/ • Fautin, Daphne G. and Romano, Sandra L. 2000. Anthozoa. Sea Anemones, Corals, Sea Pens. Version 03 October 2000. http://tolweb.org/Anthozoa/17634/2000.10.03 in The Tree of Life Web Project, http://tolweb.org/ • Fautin, D. G. and R. N. Mariscal. 1991. Cnidaria: Anthozoa. Pp. 267-358 in F. W. Harrison and J. A. Westfall (eds.), Microscopic Anatomy of Invertebrates, volume 2: Placozoa, Porifera, Cnidaria, and Ctenophora. Wiley-Liss, Inc., New York and other cities. • Fautin, D. G., Romano, S. L. & Oliver, W. A. Jr., 1999: Zoantharia - Sea Anemones and corals. The Tree of Life • Fedonkin, Misha A. and Waggoner, Benjamin M. 1997. The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism. Nature 388(6645): 868-871 • Foster, Merrill W. 1979. Soft-bodied coelenterates in the Pennsylvanian of Illinois. pp. 191-267 In: Mazon Creek fossils. edited by Nitecki, Matthew H. Academic Press, New York, NY.
Works cited • Fundación Huinay, Departamento de Biología Marina, Universidad Austral de Chile Casilla 567, Valdivia, Chile • http://nationalzoo.si.edu/Animals/Invertebrates/Facts/cnidarians/ • Parker, S. P. (ed.), 1982: Synopsis and classification of living organisms. Vols. 1 & 2 --McGrew-Hill Book Company • Image: http://en.wikipedia.org/wiki/Jellyfish • Image: www.aloha.com