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Sponges
 
 
 
 
Sponges belong to the phylum Porifera, meaning pore bearing.  They really quite simple organisms, but vary greatly in both size and form.  Sponges are nearly exclusively marine.  Some are solitary individuals, and others occur in groups or colonies of individuals.  They lack internal organs and circulatory and digestive systems.  External holes or pores in the walls provide openings through which water carries food and oxygen into the cells and a larger opening at the top, the osculum, that permits the water to flow out.  Sponges are primitive, simple, multicellular, aquatic animals which first appeared in the Cambrian period, some 570 million years ago, and have survived to the present day.  Fossil sponges are most common in the Cretaceous period.  Sponges vary in size from 1 cm (0.4 inches) to more than 1 meter (3.3 feet).  They vary greatly in shape, being commonly vase-shapes, such as Ventriculites; spherical, such as Porosphaera; pear-shaped, such as Siphonia; leaf-shaped, such as Elasmostoma; and branching, such as Doryderma.

Sponges may be either rigid solitary individuals or colonial, consisting of many
individuals, and mat-like.  Since all sponges live attached to the bottom, they must necessarily live in quite waters, because sediment in agitated water would tend to clog these openings.  If this occurred, injury to the delicate tissue within the organism could result.

The classification of sponges is primarily based on the composition of the skeleton.  In general, there are two kinds of cells in the sponge body.  One lines the internal cavity and which, by making motions with hair-like flagella, creates food-carrying water currents.  The another forms the outer part of the body wall and sometimes secretes skeletal structures of silica (siliceous), or calcium carbonate (calcareous), called spicules.  Some have skeletons comprised of many needle-like single or multi-rayed spicules.  These spicules may be fused together to form a solid framework.  The spicules are what give the sponge it ability to be preserved as a fossil.  Spicules from the fossils of Cambrian sponges are indistinguishable from those of similar living sponges.
 

The natural bath sponge is not commonly preserved as a fossil because it lacks hard spicules, but Heliospongia had a preservable skeleton.  Heliospongia had lumpy siliceous spicules that interlocked to form its thick cylindrical wall.  The pores were present along the outside of the cylinder, and the osculum at the upper end.  The Heliospongia is a sponge that does not bear much resemblance to what most people them of when the word sponge is mentioned.

This sponge has two pecularily-shaped fossils.  These distinctive rows of bead-like spherical chambers are the calcareous skeletal remains of the sponge Girtyoceolia.  The entire animal, of which only small parts are seen here, lived in shallow clear water, attached to the bottom.  They branched upward from the base, and bore numerous spout-like openings on the outer walls of the chambers through which water currents passed, bringing in food and oxygen and carrying away wastes
This  is the sponge Amblysiphonella.  It is similar in structure to Girtyocoelia, but differs in that the chambers are less bead-like or globular, and it has an axial tube seen as a circular aperture in the specimen.  This specimen is rust-colored because the original skeletal material has been replaced by an iron-rich mineral.  Amblysiphonella is restricted to Upper Pennsylvanian rocks, such as Topeka Limestone
The fossil record of sponges is not abundant, except in a few scattered localities.  Some
fossil sponges have worldwide distribution, while others are restricted to certain areas. 
Sponge fossils such as Hydnoceras and Prismodictya are found in the Devonian
rocks of New York state.  In Europe, the Jurassic limestone of the Swabian Alps are
composed largely of sponge remains, some of which are well preserved.  Many 
sponges are found in the Cretaceous Lower Greensand and Chalk formations of
England, and in rocks from the upper part of the Cretaceous period in France.  A
famous locality for fossil sponges is the Cretaceous Farringdon Sponge Gravels in
Farringdon, Oxfordshire in England.  To see our collection of fossil sponges, just click on the icon below.
 
 
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