Did Paleozoic Corals Have Zooxanthellae?

The organisms are, therefore, diploblastic. The satellite ectoderm and familiar 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 phylum Coelenterata bring in no mesoderm or coelum. Epithelial, muscular, and connective tissue note all occurs within the twain primary personify layers. In addition, phylum Coelenterata have evolved various specialized cells. These include the con cells, or nematocysts (Clarkson, 1986, p. 80).

One general feature of the Phylum Cnidaria consists of polymorphism. This basically involves the occurrence of different carcass impresss within the same species all sequentially, at different life cycle stages, or within a colony. In Cnidaria, two basic body casings prevalent: these include the fixed polyp and the free-swimming medusae. The cnidarian life-cycle whitethorn be generally characterized by successive generations of these two body types. For example, the polyp may give rise asexually to the medusae; this body type may then reproduce sexually to form zygotes and develop back into polyps. Among the more specialized members of the phylum, however, body type alternation may be completely curb (Clarkson, 1986, p. 80).

The muscle cells of Cnidaria allow the organisms to contract both longitudinally and transversely. They can alike bend, eject matter, and activate their tentacles. The animals' nerve networ

The class Actinozoans are divided into the following three subclasses: Ceriantpatharia, Octocorallia, and Zoantharia (Clarkson, 1986, p. 85). The corals belong to subclass Zoantharia. late(a) species occur worldwide at depths ranging from 0 to 2750 meters.

The scleractinians fall into two main ecological subgroups. These include the ahermatypic and hermatypic corals. Ahermatypic corals have no dependent relationships. They therefore have few environmental restrictions and may be found as deep as 6,000 meters.

Various subdivisions of Phylum Cnidaria include the following: Class Hydrozoa, Class Scyphozoa, and Class Anthozoa. Of these, Anthozoa is the largest class currently in existence: indeed, the group has everyplace 6,000 living species, including the corals.

These solitary and colonial Cnidaria are solo marine. Moreover, within this class, the medusoid body type is entirely suppressed; the polypoid coral is fully capable of sexual reproduction (Clarkson, 1986, p. 82). amongst successive polyp stages, Anthozoa exist as free-swimming larvae, or planulae.

Corals of the Order Scleractinia secrete an aragonite exoskeleton. Typically, the skeletons' septa are inserted between the mesenteries in multiples of six. After the first six prosepta have formed, "successive cycles of 6, 12, 24 metasepta are inserted in all six quadrants (Clarkson, 1986, pp. 103-104)." It is this pattern of septal insertion which immediately distinguishes the Scleractinia from the Rugosa. In addition, scleractinian structure tends to be luminosity and more porous than that of rugose corals. Such differences have light-emitting diode various authors to postulate that Scleractinia's ancestors were not Paleozoic corals, but preferably sea anemones (Clarkson, 1986, pp. 103-104).

Members of the Phylum Cnidaria have no specialized excretory, respiratory, or circulatory structures. In fact, their single body cavity, or enteron, has nevertheless one opening. This serves as both the mouth and the anus, and is
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