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Science Olympiad
Cnidaria
Cnidarians include jellyfish, sea anemones, and corals. Cnidarians are more complex animals than sponges in that they have tissues; however, these tissues are not organized into organs. Cnidarians have sac-like bodies with two cell layers separated by a jelly-like layer (mesoglea). An outer layer of cells (ectoderm) encloses a sac-like body and extends into tentacles surrounding a mouth at one end of the organism. The tentacles are equipped with stinging cells (nematocysts). A layer of cells (endoderm) lines the inner cavity (enteron) that functions as a digestive cavity. Prey is disabled by stinging cells (nematocysts) and pulled through the mouth and into the cavity by the tentacles where it is digested. Waste products exit out the mouth. In corals, the ectoderm secretes a skeletal material.

Polyp & Medusa

Cnidarians have a primitive nervous system, muscular system, and a reproductive system. Cnidarians alternate between polyp and medusa life stages. Polyps are a sessile stage and reproduction is accomplished though asexual budding. The buds become free-floating medusa. Medusa release sperm and eggs to produce larvae through sexual reproduction. The larvae eventually attach to a surface and become a polyp. Jellyfish spend most of their life in the medusa stage, while coral, hydra, and sea anemones spend the majority of their life in the polyp stage.

Paleontologist are interested in corals because they can be important reef builders, provide clues to water conditions, water depth, climate, and latitude. The orders of stony corals are of particular importance to the paleontologist.

Tabulate Corals

Tabulate corals (order Tabulata) make their first appearance in the early Ordovician. Tabulate corals were colonial, building closely packed calcite tubes (corallites) with horizontal dividers (tabulae). Favositid corallites are packed into a honeycomb-like structure. Favositid corals were important reef builders during the Silurian and Devonian. Halysitids corallites were linked like chains and are often referred to as chain corals. Halysites was an important reef building coral during the Silurian. The tabulate coral Lithostrotionella is the state gem for West Virginia.

Rugose Corals

Rugose corals (order Rugosa) make their first appearance in the mid-Ordovician. Rugose corals are solitary or colonial. Corallites of rugose corals are subdivided by vertical walls (septa). The polyp lived in the cup-shaped top of the corallite and grew upwards. Solitary rugose corals are called horn corals. Hexagonaria is a colonial rugose coral that was an important reef builder during the Devonian. The Petoskey Stone is the state stone for Michigan and represents the fossil Hexogonaria percarinata. Tabulate and Rugose corals met with extinction in the Permian.

Hexacorals

Hexacorals (order Scleractinia) may have evolved from a rugose coral. They make their first appearance in the mid-Triassic and have been major reef builders up to the present day. To learn more about the history of reef building visit the introduction to each time period in our museum. Agatized coral, representing a variety of fossil hexacorals from the Eocene, is the state stone for Florida.

Science Olympiad Fossil Event

The 2016 Science Olympiad Fossil List inlcudes the class Scyphozoa (jellyfish) and the class Anthozoa (Horn and Colonial corals). The following Anthozoa genera are listed: Heliophyllum, Favosites, Hexagonaria, Halysites, and Septastraea.

 

Favosites
Favosites
Top View Showing
"Honeycomb" Corallites

Mississippian Period
Ohio, USA

Corralites are 2 mm in diameter
Favosites
Favosites
Side View Showing Tabulae
Mississippian Period
Ohio, USA
Spaces are 1mm or less

Halysites
Chain Coral
Halysites
Note Trilobite pygidium
Silurian
Oeland, Sweden
Pygidium is 1 cm long


Halysites
Close Up
Halysites
Note Trilobite pygidium
Silurian
Oeland, Sweden
Pygidium is 1 cm long
Horn Coral
Horn Coral
Grewingkia canadensis
Ordovician
Waynesville Formation Indinana
St. Leon, IN
Hexogonaria
Hexogonaria
Devonian
Conklin Quarry
Coralville Iowa
Corallites 0.5 cm diameter

Fossil Coral
Oligocene
Withlacoochee River
Tampa Bay, Florida

Fossil Corollites
Oligocene
Withlacoochee River
Tampa Bay, Florida


Halysites catenularia
Silurian
Racine Formation, Wisconsin

15 cm across x 11 cm tall


Halysites catenularia
Top View


Bibliography

Prothero, D.R. (1998). Bringing Fossils to Life: An Introduction to Paleobiology. New York: McGraw-Hill.

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