Coral or Sponge; a process of identification

Sponge or Coral (Mystery Florida Fossil)

Sponge or Coral (Mystery Florida Fossil)

I’ve been very perplexed by this Florida fossil whether it’s a coral or sponge, but my sense of curiosity doesn’t give up easily.  Follow along as I come to a conclusion as to its identity.  To begin with, the mystery fossil  possesses meandering ridges resembling the various types of brain corals, yet it is dotted with numerous protruding openings very much like the encrusting  sponge species below, also found in Florida.

Brown Encrusting Octopus Sponge Source:

Brown Encrusting Octopus Sponge
Source: Wikipedia Commons



Florida Brain Coral Fossil


The problem with the encrusting type of sponge is that they cover hard surfaces much the same way in which moss covers the ground.  I don’t know if this type of sponge, with its unique growth pattern, would break loose and end up on a beach where my mother-in-law, Winkie, picked it up in Florida during the 70’s and 80’s.

Rose Brain Coral Fossil

Rose Brain Coral Fossil

Pink Lumpy Sponge Source:

Pink Lumpy Sponge
Source: Wikipedia Commons









If you’ll notice, the “rose brain coral” above has a few pitted holes like the mystery fossil but not nearly as many; and if you’ll also notice, the “pink lumpy sponge” to the right possesses a pattern of ridges, but only sort of like the mystery fossil.  Hmmmm . . . a point I’d like to make for a second here, is how this demonstrates what fossil hunters do. They learn to observe things with a keener eye in order to identify their findings. Anyway, we’ve concluded our mystery fossil has similar characteristics as the above corals and sponges, but not exactly the same as any of them.

We’re on the bloodhound trail, let’s continue observing.  On the one hand, the mystery fossil is quite lighter and airier compared to the other Florida corals in my collection and it has more openings visible on all sides which leads me to think it could be a sponge. But, the patterns of ridges, plus the color, shape, and texture is quite similar to the other corals from the collection.

Christmas Tree Tube Worms Source:

Christmas Tree Tube Worms on Coral Source: Wikipedia Commons


Tube Worms On Clam

Tube Worms On Clam









So, if the mystery fossil, on most levels, appears to be a coral with the one exception of the deeply pitted holes, what could have caused those holes and why so many? Observe the Christmas tree tube worm image above. The tube worms have completely covered the top of a coral.  Could they have made the holes in question? I’ve decided not because the openings on the mystery coral look quite different from the tube worm burrowing on the clam fossil above. I’m no expert, but I decided the mystery fossil is a type of coral, likely related to the brain corals. Feel free to disagree in the comments if you know of think otherwise.

Check out the tube worms link to the right listed under CLASSIFICATIONS to learn more about them and how they can actually be quite pretty.


Comparing Two Star Coral Species

From the Upper Jurassic to recent times The Great Star Coral, Montastrea cavernosa, forms sizable massive heads and sometimes plate-like structures. The polyps can be quite variable in color, from green and brown to bright red.  It’s a dominant species at moderate depths off Palm Beach County, Florida and the windward shore of  Barbados.  It can also occur in the Caribbean, the Bahamas, the banks off the Texas coast, Bermuda, Brazil and off western Africa.  It’s one of the deepest occurring corals found at depths from only a few meters to at least 90 meters.

Montastrea cavernosafossil

Montastrea cavernosa (The Great Star Coral) fossil


Monstastrea cavernosa (star coral) fossil side view

The fossil above is another in my possession from my late mother-in-law Winkie (Winifred) Mirto. She gathered a small collection off the Florida coast before protection laws forbid people to do so.

1983 Ft. Lauderdale Florida Winky and Joe

1983 Ft. Lauderdale Florida
Winkie and Joe

Threats to Montastraea cavernosa include coral bleaching, ocean acidification and coral disease, especially black band disease and white plague.

Choose Your Sunscreen Carefully

Montastraea are hermatypic, containing symbiotic algae called zooxanthellae that help nourish it, provides it oxygen and dispatch waste.

Montastraea, cavernosa with open tentacles source:

Montastraea, cavernosa with open tentacles


Kingdoms : Animalia

Phylum:  Cnardia (Marine group with stinging cells

Class:  Anthozoa (Flower Animal)

Order:  Scleratinia: (Modern species of Stony Coral)

Family:  Faviidae (Generally spherical shaped grooved surfaces)

Genus:  Montastraea

Species:  cavernosa (above) annularis (below)

Montasrea annularis

Montastrea annularis (Boulder Star Coral) fossil

Montastaea annularis commonly known as the Boulder Star Coral, co-occurs in near abundance with M. cavernosa only it dominates in the Caribbean regions. It also grows in varying depths down to 80 meters and grows in varying colony shapes (heads, column, or plates) in response to differing light conditions.


Montastraea annularis

Competition between the cousin genera has shown them to adapt longer sweeper tentacles in order to attack intruding corals.


Montastrea cavernosa Source:

Montastrea cavernosa