It was embedded in a fragment of chalk that had fallen from the cliff, so it dates from the Upper Cretaceous Period, 95 to 65 million years ago. I drew it for my 1996 book Yorkshire Rock, A Journey Through Time but since then the chalk that surrounded it has split into shards. The collar of the smaller sponge has disintegrated too.
Sponges were common as the age of the dinosaurs drew to a close. They had a sac-like body with a central cavity known as the cloaca.
The nearest species that I can find is Laosciada, a mushroom-shaped lithistid, a kind of demosponge, informally referred to as a calcisponge. It lived in deep water, between 100 and 400 metres.
The skeleton of the collar of this sponge is made up of interlocking spicules, which look like little pyramids in close-up. They’re made of silica which, remineralised, forms the layers of flint found in the chalk.