Paleo Lab 4 - Brachs

Paleo Lab 4 - Brachs - PALEO LABORATORY # 4, PAGE 1 PALEO...

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PALEO LABORATORY # 4, PAGE 1 PALEO LAB # IV - CNIDARIANS, BRYOZOANS AND BRACHIOPODS A. Phylum Cnidaria (Coelenterata) The cnidarians are a group of aquatic animals which include the corals, sea anemones and jellyfishes. These saclike animals have inner and outer body layers that are separated with jellylike tissue. The cnidarians are characterized by two distinct features: (1) they are composed of tissues not constituted into organs and (2) their parts are arranged on a radially symmetrical plan. Throughout their history the cnidarians have been aquatic. Although they are predominantly marine, there are numerous freshwater forms. Most are carnivores that capture their prey by means of stinging cells. The individual coelenterate animal is one of two definite morphological types (1) a hollow, sac-like polyp or (2) an umbrella-shaped medusa. Polyps are commonly attached and frequently secrete a skeleton. Medusae are usually free-swimming and without skeletal hard parts. The colonial habit is very well developed among the Cnidaria, including the reef-building corals, which during the geologic past have built and are still building, great calcareous reefs partly composed of their stony skeletons. However, there are and have been many coelenterates without the colonial habit; for example the cup corals of the Paleozoic and the freshwater hydra of the present. 1. Class Hydrozoa The hydrozoans consist of freshwater or marine cnidarians in which the generations alternate between the mostly colonial polyp generation and a medusa stage. However, in most forms the polypoid generation is dominant. Most hydrozoans are marine, although the common freshwater genus Hydra is an exception. The most common group of modern hydrozoans are the hydroids, but they have a chitinous skeleton which is typically not preserved in the fossil record. The hydrozoans that typically fossilize are marine forms bearing calcareous skeletons belonging to the orders Milleporida and Stylasterida. EXERCISE # 1 - Observe the fossil hydrozoans Plumalina plumaria (TSU IP 047) and the siphonophore fossil (TSU IP 413) . Do these fossils represent polypoid or medusoid generations? 2. Class Scyphozoa The Scyphozoa, or jellyfish, are exclusively marine cnidarians which spend most of their life cycle as free-floating medusa. Although jellyfish are capable of limited swimming they are primarily planktonic, moving where the currents take them. These animals capture their food by means of dangling tentacles. The oldest-known scyphozoans are found in the Late Proterozoic- age Ediacaran fauna. Approximately 2300 genera of jellyfish have been described. EXERCISE # 2 - Observe the scyphozoan specimens provided in lab (TSU IP 048, IP 049, IP 419, IP 427). Do these represent polypoids or medusoids? 3. Class Anthozoa
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This note was uploaded on 01/16/2012 for the course GEOL 305 taught by Professor Dr.phillipmurphy during the Fall '10 term at Tarleton.

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Paleo Lab 4 - Brachs - PALEO LABORATORY # 4, PAGE 1 PALEO...

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