Paleo Profiles

Astraeospongia meniscus

Fossil sponge

Fossil sponge

I can remember the first time I saw an Astraeospongia.
I was watching a slide show in paleontology class. I found this type of fossil intriguing because it seemed counterintuitive to expect to find a fossil sponge – especially one that was so well preserved. After all, they have no bones, teeth, or shells – the hard parts of animals that are normally preserved in the fossil record.

Through my biology and zoology classes, I was taught that the sponges (members of Phylum Porifera) represent the most basic level of organization in the Animal Kingdom. Sponges are a collection of a few types of specialized cells. They do not possess true tissues, organs, or even organ systems like we do.

Most sponges are marine (live in ocean) and sessile (live attached to the bottom or to some object). Water enters the sponge’s tiny pores, called ostia. As the water circulates through the sponge, small food particles and plankton are filtered and eaten. Water then leaves the sponge through large openings at the top called oscula (osculum – single).

Most sponges have structures called spicules that are used for structural support. They can be made mostly from silica or calcium. Spicules, the star-shaped structures evident in the specimen in the photo, help us to immediately identify this as a poriferan (sponge).

There are many “tricks” that can be performed by a variety of animals. Sponges have, perhaps, the most amazing “trick” of all. Some sponges can be blended, passed through a fine sieve and back into seawater. Not only do the cells survive, but within a matter of hours, they begin to come back together and form a new sponge.

The fossil sponge in this Paleo Profile
and the prize sponges were collected in Decatur County, Tenn. The Silurian age Brownsport represents a marine environment that covered west-central Tennessee some 425 million years ago.

Your question for this Paleo Profile
is “What is the name of the popular Nickelodeon poriferan with an echinoderm as a best friend?” Hint: He lives in a pineapple at the bottom of the sea. Be one of the first three to call curator Amy Rhudy at the Blount County Memorial Museum at 625-6905 with the correct answer and win an Astraeospongia meniscus.