Classes of the Phylum Porifera (currently in Atlas)




What is a sponge?
Sponges are the simplest multicellular life forms to inhabit the oceans. They are made up of loosely integrated assemblages of cells which secrete a porous skeleton. The skeleton of a sponge is a simple cone or cylinder with a hollow central cavity. The organism has numerous pores (ostia) throughout, which bring in water and nutrients. Sponges also have organic fibers (spongin) which is a high-sulfur organic compound. They can also contain needle-like spicules which are mineralized with either silica or calcite. In the fossil record, the spicules are commonly preserved.

Where are sponges found?
Sponges are among the oldest living organisms on earth. In recent years, sponges from the Class Demospongia have been found in strata dated to be 635 million years old (Ediacaran period). Therefore, sponges have adapted to live in a wide array of environments. Sponges have a worldwide distribution, from the polar regions to the tropics. The majority of sponges can be found in temperate to tropical areas. There are both freshwater and saltwater species. Most sponges live in clear, quiet, calm waters, since the organisms are filter feeders and suspended sediment clogs their abilities to breathe and eat. A large group of sponges can be found on hard substrates, such as rocks, but some have been known to attach themselves to soft substrates with a root-like base.

Classes of Sponges
There are six classes of sponges. Class Hexactinellida are those organisms which are called ‘glass sponges’. They are found in shallow to deep marine, and their spicules are made of silica at 90-degree angles. Class Calcarea are calcareous sponges with spicules that have a variable number of rays. Typically, these sponges live in shallow marine environments. Class Demospongea are the most common sponges, with spicules that are made of the organic compound spongin. They live in both marine and freshwater conditions. Class Sclerospongea are sponges which are made of calcite, with spicules made of calcite or silica, or absent. Class Stromatoporoidea are massive, layered, calcareous sponges. They are identifiable by laminae connected by pillars, and mamelons (surface bumps) and star-shaped astrorhizae. They were the major reef builders during the Silurian-Devonian.

Which sponges can be found near Cincinnati?
The two classes of sponges which can be found in Cincinnatian strata are the Demospongia and Stromatoporoidea.