That might be the snail... IDK. Why the UGH? Is it a bad snail? I don't know anything about that snail.

As for the sponge. It is a cryptic sponge that tends to grow and spread in established tanks. High flow and low light are the where it likes to live. It will not survive in high light.

Tom

By the way, I wouldn't worry too much about that snail shell. It looks to me like it was an empty shell that was part of your substrate (JMHO).