Did Paleozoic Corals Have Zooxanthellae? The Ph

The Phylum Cnidaria can be traced from the late Proterozoic to the Holocene. Several major geologic boundaries occur throughout that span of time. The temporal intervals are often based on biological extinction and radiation events. For example, the Paleozoic begins at the Precambrian/Cambrian boundary and ends at the Permian/Triassic boundary. Analyses of carbon-12/carbon-13 data suggest that these boundaries were characterized by major alteration of the earth's biomass. Various Paleozoic Cnidaria corals became extinct at the end of the Permian. Whether or not these extinct corals gave rise to later orders remains uncertain. It seems doubtful though that primitive Paleozoic corals could have developed the advanced symbiotic algal relationships characteristic of their more modern counterparts.

The medium-sized Phylum Cnidaria includes the corals, sea anemones, and jellyfish. These aquatic invertebrates typically have primary radial symmetry and are, for the most part, anatomically simple. Unlike higher animals, they have no specialized cells grouped into organs. Rather, their different cell types occur in only two body layers; they are, hence, referred to as diploblastic. The outer ectoderm and inner endoderm develop from the embryo and are divided by a jelly-like, middle noncellular layer. At the base of the outer cell layer, this structureless mesoglea contains a simple nerve net. The Cnidaria have no mesoderm. Epit

. . .
us than that of rugose corals. Such differences have led various authors to postulate that Scleractinia's ancestors were not Paleozoic corals, but rather sea anemones (Clarkson, 1986, pp. 103-104). The scleractinians fall into two main ecological subgroups. These include the ahermatypic and hermatypic corals. Ahermatypic corals have no symbiotic relationships. They therefore have few environmental restrictions and may be found as deep as 6,000 meters. In contrast, the endodermal cells of hermatypic corals contain symbiotic algae. Algal symbiosis may be defined as "an association between a host organism and one or more species of unicellular algae" (Cowen, N.d., p. 431). Such interrelationships are actually quite common in modern seas, particularly among lower invertebrates in nutrient-poor environments (Cowen, N.d., p. 432). Typically, the algae--which may include either dinoflagellates or zooxanthellae--occur within hermatypic cnidarians in large numbers. They are thought to enter the host by normal routes of ingestion. Rather than becoming food themselves, however, the algae multiply intracellularly and coexist with the corral. Three ways in which zooxanthellae interact with cnidarian hosts include the following:
. . .

Some common words found in the essay are:
Cowen Nd, Phylum Cnidaria, Oliver Coates, According Lang, Cretaceous/Tertiary Magaritz, Scleractinia Rugosa, Middleton Murray, Triassic Ruedemann, Late Paleozoic, Anthozoa Anthozoa, cowen nd, clarkson 1986, paleozoic corals, symbiotic algae, erez 1978, oliver coates 1987, hermatypic corals, rugose corals, phylum cnidaria, coates 1987, oliver coates, cited cowen nd, erez 1978 202, clarkson 1986 80, blatt middleton murray,
Approximate Word count = 2561
Approximate Pages = 10 (250 words per page)

More Essays on Did Paleozoic Corals Have Zooxanthellae? The Ph