Geology 105 - Paleontology
 Course Syllabus  Course Schedule   Assignments  Course Handouts  Critter Charts   Department Home Page  Kusnick Home Page

Lab #2: Sponges and Corals

At the end of this lab, you should be able to:

  1. 1. Identify a fossil as a sponge, archeocyathid, rugose, tabulate or scleractinian coral.
  2. 2. Know the skeletal structure and material of each of these animals.
  3. 3. Know the ecological characteristics of each of these animals.
  4. 4. Know the geologic range of each of these groups.
  5. 5. Know a few important genera (mentioned by name in this handout) for each group.

Display

Look carefully at the display specimens. Use your Critter Chart and textbook to help you find the important morphological features of each group.

Sponges: look for pores, spicules, internal cavity (spongocoel), osculum (not all features are visible in each specimen)

1.  Modern desmosponge.  Find the pores, and notice the thread-like spicules made of protein.  This sponge grew up around a bryozoan colony, which you can see at the bottom and top of the specimen, and a little mussel.

2.  #507 Girtyocoelia.  This little Paleozoic sponge is calcareous.  It grew in bulbous chambers around a central tube, as shown in the diagrams.

3.  # 2004 Astraeospongia.  Another Paleozoic calcareous sponge.  Find a star-shaped spicule.  The Sponge was a dish-shaped mass of organic material around these spicules.  This fossil is essentially the mud that filled the depression formed by the dead sponge, including the spicules of the sponge and other debris, including tiny plates from a crinoid.

4.  #1622 Astylospongia.  This is a siliceous sponge.  In the picture, notice the six-armed spicules that form a solid network.  In our sample, the spicules have recrystallized and are hard to distinguish, but you can see the pores where the spicules meet.

5.  #90 Dystactospongia.  This Paleozoic sponge is a desmosponge.  The original protein spicules have been replaced by calcite in this specimen. 

6.  #506 Heliospongia.  ANother Paleozoic desmosponge.  Notice the spicules arranged around the pores, and the osculum running through the specimen.

Archeocyathids (#674):

7.  #2005 & #2006: Notice the cone-in-cone construction with septa between the cones.  The organism had pores in each cone and a holdfast at the bottom.

Corals

Rugose corals

8.  Here are a variety of rugose corals to demonstrate some of the range in shape and size: #4, 18, 50, 2007, 2008.

9.  #1698 Zaphrentis: This sample has beautifully preserved septa.  In life, the organism draped its digestive tissue around the septa to increase the digestive surface area.

10.  #1818 Heliophyllum:  Notice the  nicely preserve cup (calyx) where the body of the organism sat, with its tentacles rising above the top of the skeleton.

11.  Two sections through a rugose coral:

12.  #1103 and #841 Heliophyllum: Some rugose corals grew to be very large, requiring very massive skeletons.  In the modern world, all invertebrates with large skeletons of calcium carbonate have symbiotic algae called zooxanthellae living in their tissues to help them produce enough sugar (and thus energy) to produce so much mineral skeleton.  We assume that invertebrates of the past with large skeltons probably had similar symbionts.

13.  #2009 Pachyphyllum: Most rugose corals were solitary, but a few grew in colonies.

Tabulate Corals

14. #1416, 62 & 1405,  species of Favosites:  These specimens show the structure of a tabulate colony.  Notice the hexagonal corallia on the surface - the holes the polyps lived in - and the tabulae on the side - the floor of the polyp's cup.  As the colony grew, each polyp moved up and built a new tabula - floor - underneath it.

15.  #514, 72, 1186 & 844 Favosites, and #515 Alveosites: Some tabulate corals have a  honeycomb structure.  Each polyp lived in the hexagonal spaces.

16. #82 Protarea, #521 Synaptophyllum & #1131 Aulopora: Other tabulates have different forms.  Here is an example of a tabulate coral (82) where the corralites are a fancy shape - like a flower - and two others (1131 & 521) made of intertwined tubes.

Scleractinian Corals

17.  # 1651 Astrhelia, #1942, and unnumbered specimen: Most scleractininan corals are colonial.  Often the polyps are very tiny, and locating the individual coralites is difficult. The polyps on #163 would be about a half inch across, while the polyps on #1942 were millimeters across.

18.  #1941 Manicina and #461 Flabellum.  Other scleractinians are solitary, with a single polyp.  The polyp for specimen #1941 was several inches across.

19.  #468 Cladangia: Recent scleractinian corals are easy to recognize because of their aragonite skelton and distinctive shapes.  Geologically older scleractinians can look very much like colonial rugose corals; if the aragonite has recrystallized to calcite, as in this sample, it usually takes a specialist to recognize the coral as a scleractinian.  Fortunately for you, almost all Cenozoic coral is scleractinian, since rugose corals died at the Permian boundary, and only one family of tabulates made it out of the Paleozoic (and went extinct in the Eocene)

Questions:

Answer these questions about specific specimens:

Sponges
1. Specimen #156. Hydnoceras was an important reef builder in the latest Devonian. Does it show evidence of a well-organized skeleton? Look at the pattern of spicules. Is this a siliceous (Hexactinellida) or calcareous (Calcarea) sponge?



2. Specimen #142. Astreospongia is an important index fossil for the Silurian and Devonian. Find and sketch a spicule. Does this sponge show evidence of a well-organized skeleton? Is this a siliceous or calcareous sponge?



3. Specimen #505. Look at the cross-section through this sponge. Trace the path water would take through this animal. What is the mode of preservation for this fossil?


4. Specimen #358. Look carefully at the surface structure and the cross-section of this sponge. Do you see the external structure reflected in the internal structure? What kind of preservation is this? (You might want to compare this sample to #505).



5. Specimen #166. Examine this small spherical sponge carefully. How could you tell this is not just a pebble?



6. Specimen #23. This is a very early sponge fossil. Find spicules in this sample. How are they preserved? From the shape of the spicules, do you think this is more likely to be a silica or calcareous sponge?



Stromatoporoid
7. Stromatoporoids were very important reef builders of the Silurian and Devonian, but are otherwise mysterious. Paleontologists have described them as everything from cyanobacteria to their own extinct phylum, but their closest affinities seem to be with a small group of encrusting sponges, the Sclerospongea (not a name you need to remember). Contrast this stromatoporoid (1614) with the stromatolite (162). Stromatolites are fossils of algae, where sediment accumulated on the sticky bodies of single-celled algae forming thin layers. What are the morphologic features that let you distinguish the stromatoporoid form the stromatolite?

Now compare #154 & #73 with the other samples.  One is a stromatolite, one is a stromotoporoid.  How can you tell which is which?

 

Archeocyathid
8. Specimen #1613. Orient this sample as the organism would have been in life. How did water move through this specimen? Why are archeocyathids though to be closely related to sponges?

 



Corals
9. Specimen #839 is a mass of gregarious rugose corals which have grown up next to each other. (Gregarious means the organisms live in groups without being truly colonial - without being connected by soft tissue. Human beings, dogs, prairie dogs, lions are all gregarious animals).
Specimen #1416 is the tabulate coral Favosites, a truly colonial coral.
Is specimen #888 a rugose or tabulate coral? To answer this question, think about what structural features distinguish the two groups. Do you think this organism was gregarious or colonial (a tricky question when no soft tissue remains)? Cite your evidence for both questions.

 



10. Specimen #1698, #461. One of these is a solitary rugose coral (Zaphrentis); the other is a solitary scleractinian. Which is which? Cite your evidence.

 



11. Specimen #516. Look carefully at the internal structure of this rugose coral . What are the lines running across the organism? How did these structures change over the lifetime of the organism?

 



12. Specimen #1417/1418. This sample contains 2 corals. What group does each belong to?



13. Specimen #829. Does this sample represent catastrophic burial of a living community, or an accumuloation of dead material? What is your evidence?

 



14. Specimen #482. This is a colonial scleractinian coral. In life, where would the polyps be located? What skeletal material is this? What is the mode of preservation?



15. Specimen #1452. This is a solitary rugose coral. Do you think this coral had zooxanthellae? Why or why not?



16. Specimen #890. What kind of coral is this?  Is it solitary or colonial?  How is this fossil preserved?