Sponges are animals. And what most of us know as sponges, are really just the skeletons of sponges, says Christian Vaterlaus. He is the owner of a sponge farm in Zanzibar.

About "My favorite"

With all the talk of endangered species, the value of biodiversity and the usefulness of ecosystems, we sometimes forget why plants and animals are really worth protecting: because we love them, or depend on them for our own wellbeing. People from all walks of life and in all parts of the world have a favorite species. The reasons are many - perhaps because it is beautiful, or fascinating, or it helps them secure a livelihood. Meet some of these people and their favorites in our series "My favorite."