Class Schyphozoa

Class Schyphozoa - rugose and tabulate corals went extinct...

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Class Schyphozoa: True Jellyfishes ( Aurelia ) The medusal stage is dominant in jellyfish (Figure 15) and other members of this taxonomic class. The polyp remains small and inconspicuous. Jellyfishes also serve as food for larger marine animals. The Fossil Record of Cnidarians The fossil record of cnidarians is very good for hard-part containing corals, but usually not as good for soft-bodied forms like jellyfish. Corals become dominant reef- building animals during the Ordovician , and continue their importance today. Corals, which had appeared possibly as early as the late Proterozoic (precambrian, more than 540 million years ago), diversified into a number of groups during the Silurian times. Tabulate corals and rugose corals were major components of the new, larger reefs built during the Silurian through Permian (the Permian ended 250 million years ago). Rugose corals included the horn corals, while tabulate corals were colonial. Both the
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Unformatted text preview: rugose and tabulate corals went extinct at the close of the Permian period. Figure 16 shows a coral collected in central Arizona. Near the end of the Devonian a mass extinction occurred. This one was more severe on marine creatures than on the newly established terrestrial forms. The corals were quite seriously decimated, and the return of extensive reef building did not occur until the Triassic with the evolution of a new group of reef-building corals, the scleractinians (shown in Figure 17). Corals were much restricted after the Devonian crisis and the large reefs of the Devonian were replaced with smaller reefs known as patch reefs. The role of corals in these new reefs was much reduced from what it had been in earlier times. Coral reefs, which had been decimated by the Carboniferous extinction returned to prominence with the evolution of new groups of reef-building animals and algae....
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Class Schyphozoa - rugose and tabulate corals went extinct...

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