Phylum Cnidaria
Cnidarians, formerly known as Coelenterates, range from sessile (attached to the sea floor), like the sea anemone, to freeswimmers, like the jellyfish. They are aquatic and most live in the marine environment. Sessile coelenterates or polyps
(e.g. corals) live in colonies or are solitary, living alone. The free-swimmers like the jellyfish are called medusa.
Cnidarians contain specialized cells called cnidocytes to help the organism take their prey. The name Cnidaria is derived
from these cells.
Commonly, Cnidarians are found in warm waters; however, some live to depths of 6000 m and in temperatures that go as
low as 1 degree centigrade. Cnidarians have been around for about 700 m.y. or before the Cambrian. Several fossils of
the Ediacaran fauna may be Cnidarians.
There are 3 classes into which coelenterates fall:
1. Scyphozoa (jellyfish)
2. Hydrozoa (includes stromatoporids)
3. Anthozoa (corals and sea-anemones)
We will focus on the class Anthozoa. These organisms are solitary or colonial and they have a body type known as a
polyp. Usually cylindrical, the polyp has a mouth at the top end and tentacles that surround it. Food is passed to the
mouth by these tentacles. Approximately two-thirds of the total Cnidarians belong to Anthozoa.
The class Anthozoa is subdivided into two subclasses:
1. Octocorallia
2. Zoantharia
Zoantharia in turn includes three important orders:
1. Scleractinia (reef-building corals
2. Rugosa--now extinct
3. Tabulata--now extinct
Rugosa (extinct)--were solitary or colonial and most are found in limestone suggesting that they probably lived in
shallow warm water. A few solitary horn-type are found in dark claystones and mudstones. These probably lived in
deeper and quieter environments. They appear in the Middle Ordovician, are common in the Silurian and they
disappeared in the Permian.
The name Rugosa comes from the wrinkled ridges (rugae) on the thecae. Tabulae in these corals are successively
secreted by a layer of cells at the base of the polyp as it grows and moves upward.
Scleractinia (alive today)--are solitary or colonial and first appear in the Middle Triassic, were important in the Jurassic
and are abundant today. Today, corals are found in warm shallow tropical to subtropical waters. Scleractinia may have
evolved from rugose corals (they have a similar appearance). However, some paleontologists believe that they may have
evolved from the sea anemone.
Tabulata (extinct)--were colonial and first appeared in the Middle Ordovician, were abundant in the Silurian and
Devonian and they disappeared at the end of the Paleozoic or in the Permian.
Tabulate corals are colonial. Especially prominent in these corals are the tabulae, hence the name Tabulata. The polyp
lives on the tabula that was formed last.
Rugose corals first evolved during the ______________
Tabulate corals first evolved during the _______________
Scleractinian corals first evolved during the _______________
Scleractinian corals are extinct T/F
Rugose corals became extinct in the Creatceous T/F
Tabulate corals became extinct in the Permian
The name Rugosa comes from _________________
Tabulate corals are both solitary and colonial T/F
Rugose corals are strictly solitary T/F
Scleractinian corals are strictly solitary T/F
Corals belong to thise phylum ________
Plot on Range Diagram
Unit A contains trilobites, tabulate and rugose corals. What is the age range for the unit? _________
Make a column and plot on range diagram
Unit A contains trilobites, tabulate and rugose corals. Unit A is a limestone
Unit B is siltstone and it overlies unit A. Unit B contains brachiopods but the trilobites are missing
Unit C is sandstone containing scleractinian corals.
What is the age of Unit A? __________
What is the age of Unit B? __________
What is the age of Unit C? __________
In what environment was unit A deposited ? _________
In what environment was unit B deposited? __________
In what environment was unit C deposited? __________
LAB
Examine the following corals and sketch only those I ask you to sketch. Important: make sure that you can
distinguish between the different orders, especially between the tabulate and the rugose corals. On exams I will
ask you to distinguish the different types of corals.
Tabulates:
213 Favosite basalticus, Devonian, New York, Onadaga ls. Favosites have long slender
polygonal coralites (columns), numerous tabulae (transverse flat plates representing the growth
of the coral), and pores on the coralites. Sketch and label coralites, tabulae, and pores
244 & 167 Syringopora multattenuate, Pennsylvanian, Kansas, Oread Fm. Note tabulae and
polygonal coralites united by transverse tubes.
119 Heliolites, Upper Silurian, Tennessee, Brownsport Fm. Heliolites have cylindrical coralites
with material composed of smaller tubes separating the coralites. Sketch a couple of coralites.
Look on the side of the sample to see the tabulae
117 Heliolite, Upper Silurian, Oklahoma. Compare with heliolite and make sure you can
distinguish the two.
Rugose Corals
155 Heliophyllum halli, Middle Devonian, New York, Centerfield ls. Note the wrinkled walls.
This is where the term "rugose" come from.
253 Caninia torquia, Pennsylvanian, Nebraska, Biel ls. Sketch the septa
344 Heliophyllum halli, Devonian, Ontario, Canada, Arkona shale. Examine
218 & 217 Lithostrotionella, Mississippian, Illinois, St. Louis Fm. This a sample of colonial
rugose corals. Note the wrinkled walls and the septa.
Scleractinia
Examine the following:
674 Acropora, Recent, North Atlantic coast
500 Astrohelia palmata, Miocene, Calvert beach, Maryland
677 Fungi sp , Philippines