[Noodle]

Bongo Shrimp, The common name of this sponge called "Ear Sponge"
Collospongia auris. You can find some informations and photo in a book called "The Modern Coral Reef Aquarium", Volume 3. Svein A. Fossa, Alf Jacob Nilsen.
You are right about this sponge is totally smooth like rubber, I also have two of them in my reef tank.
This sponge is a filter feeder but it also containes symbiotic blue-green algae, easy to keep in a coral reef aquarium. Rapidly growing; under optimum conditions this sponge will overgrow large parts of the aquarium's interior. Very well suited for a coral reef aquarium, but require very bright lighting.

Wai