Siphonia koenigi is pear-shaped or subspherical with a slender cylindrical stem that often detached during fossilisation.
It has a very wide aperture and many branching canals radiating out from the osculum, which is the funnel-shaped excretory structure.
The main body of the sponge is pear-shaped, originating from a slender cylindrical stem.
The sponge would have lived on the sea floor in the deep chalk sea. Sponges feed by drawing water which they pump through a system of canals and chambers containing flagellae. The water is pushed out through a central funnel.
Siphonia was typically about 50–60mm in height but could be much larger.