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Go to the key ---INDEX---
Major Phyla
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General fossil discussion
Geologic time
Phylum COELENTERATA (the corals)
This phylum includes three classes: the hydras, Hydrozoa; the jellyfishes,
Scyphozoa; and the corals, Anthozoa. This last class is by far the
most important geologically. The phylum is composed of multicellular,
radially symmetrical, mostly marine organisms with differentiated tissues.
Class ANTHOZOA
This class includes sea anemones, sea fans, sea pens, sea feathers
and corals. This last group, exclusively marine, ranges from Ordovician
to Recent. Because of their extensive skeleta, corals have an excellent
fossil record. Three orders within this class are particularly important.
Order RUGOSA (horn corals)
Corals of this order essentially look like cones with greater or lesser
taper. Septa (internal partitions) radiate from a central axis.
They may be solitary or colonial.
Order TABULATA
(tabulate corals)
This order derives its name from the diagnostic tabulae, flat plates
which provide a floor for the small (less than 1/2 cm) polyp chamber.
This colonial order was an important reef builder of the Paleozoic sea,
and in the Great Lakes region these reefs have often accumulated petroleum.
Order SCLERATINIA(modern
corals)
Triassic to Recent. They are superficially similar to compound
rugose corals. They can be distinguished from tabulate corals by
their lack of tabulae. Technically they are separated from rugose
corals by their sixfold rather than the fourfold symmetry of rugose corals.
Practically, modern corals are only rarely hexagonally appressed (packed
like a honeycomb) as are rugose corals and the septae often extend beyond
the side wall.