Paleontology Lab II

1. Paleontology Lab II CNIDARIANS

2. Phylum Cnidaria • Phylum Cnidaria • Class Anthozoa (Precambrian-Recent) • Order Tabulata (Ordovician-Permian) • Order Rugosa (Ordovician-Permian) • Order Scleractinia (Triassic-Recent) • Subclass Octocorallia (Ordovician-Recent) • Class Hydrozoa (Precambrian-Recent) • Class Scyphozoa (Precambrian-Recent)

3. Cnidaria • Cnidaria are named for stinging cells called cnidoblasts. • The name Coelenterata means "hollow" (coel) + "gut" (enteron). • Radial symmetry. • The cnidarian classes Anthozoa (corals) and Hydrozoa have calcified skeletons of aragonite and calcite and a good fossil record • The long fossil record of the class Scyphozoa (jelly fish) is comprised mostly of molds and casts. • Class Octocorallia is not well represented in the fossil record because of its poorly calcified skeletons.

4. CORALS • Corals have a hard calcareous skeleton, and may be solitary or colonial. • Colonies are composed of many polyps living together. • The skeletal parts formed by polyps are called corallites. • Each corallite is a small (several millimeters to several centimeters in diameter), roughly circular or hexagonal opening, with internal radial partitions called septae in the Rugose and Scleractinian corals. • Tabulate corals lack septae. • Geologic range: Late Precambrian (Proterozoic) to Recent • Corals live attached to the sea floor, primarily in warm, shallow marine environments.

5. Class ANTHOZOA • Geologically the anthozoans are the most important of the cnidarians because their polyps often produce calcitized skeletons that are readily preserved as fossils. • They can be either solitary or colonial. • Common forms of anthozoans include corals, sea-anemones, and sea-pens. • Anthozoans differ from other Cnidaria in that they have no medusoid stage. • They are exclusively marine and occur at various depths from shallow to deep water.

7. Order Rugose • Most rugose corals are solitary and conical • Septae are visible in the circular opening of the cone. • Some rugose corals are colonial, having hexagonal corallites with septae (such as Hexagonaria from the Devonian of Michigan). • Geologic range: Ordovician to Permian -

9. Tabulate • Tabulate corals are colonial and resemble honeycombs or wasp nests. • They lack septae. Halysites is called the chain coral because its coral tubes are attached in wavy lines resembling a chain. • Geologic range: Ordovician to Permian - all extinct.

12. SUBCLASS ZOANTHARIA ORDER SCLERACTINIA • Scleractinian corals are the modern corals. • Most are colonial, but some are solitary. • Many are reef-builders. • Skeletal material is deposited between corallites • Geologic range: Triassic to Recent.

13. Scleractinian • Scleractinian corals can be either colonial or solitary. • Their originally aragonitic skeletons have dissepiments, tabulae, and septa just as in the Paleozoic rugosans. • Although there are superficial similarities, scleractinian corals differ from rugosa corals by their skeletal mineralogy and by their method of septal insertion during growth. • Scleractinian corals also have six primary septa, but in contrast to rugosa corals, subsequent septa are added in all six of the resulting spaces. • An important distinction between the two orders is that for the Scleractinia the septa are inserted between every two pre-existing septa in later growth stages.

15. Scleractinian • Scleractinian ("hard-rayed") corals first appeared in the Middle Triassic and refilled the ecological niche once held by tabulate and rugose corals. • They are probably not closely related to the extinct tabulate or rugose corals, and probably arose independently from a sea anemone-like ancestor. • Their pattern of septa differs markedly from that of the Rugosa, being basically six-rayed. • For this reason, scleractinians are sometimes referred to as hexacorals.

20. Coral Morphology • The morphology of coral colonies can be grouped into three broad categories: • (i) encrusting forms which are often sheet-like such as this specimen. • (ii) massive forms which are domal or hemispherical • (iii) erect forms which are branching or palmate

21. encrusting forms massive forms erect forms

22. Paleoenvironments • Corals occur as framework organisms in reef environments and as important constituents in level-bottom communities. • As a group they are very sensitive to physical and chemical conditions such as fluctuating sea level, turbidity, and salinity. • Of all of these factors which may result in differing growth morphology, the overall shape of coral colonies is most responsive to water (= wave + current) energy. • However, it should be noted that the morphologic response is quite different when a coral is in a reef setting or in a level bottom setting.