“Cliona, the Parasitic Marine Sponge”

 

Some sea sponges like this 5 million year old Cliona here are parasitic, drilling into the calcium carbonate shells of other marine creatures to set up residence, in this case the host shell of a giant princess slipper snail, Grandicrepidula princeps. What we are seeing here is the fossilized trace of the Cliona sponge’s drillings on the inside of the snail's shell; a calcitic cast of the  internal mesh chambers of the sponge's drillings inside the snail's shell.  Like an ant mound casting, this represents the trace of the sponge’s home, a cast of it, inside the shell of the snail, a subfield of paleontology dealing with traces of ancient life called “ichnology”.  The drilling traces of the sponge can be so advanced and weakening the shell that the snail would have been more vulnerable to predators, making the interaction truly parasitic.You Tube Video: ​​https://youtu.be/bLPpwTlfiog