Adult form of Facetotecta. The adult form of this animal has never been encountered in the water, and it remains a mystery what it grows…

Adult form of Facetotecta. The adult form of this animal has never been encountered in the water, and it remains a mystery what it grows into.

Open the “Ecology, evolution, and paleontology” section on Wikipedia →

Source: List of unsolved problems in biology (CC BY-SA 4.0)