The Mbielu-mbielu-mbielu, or “animal with planks growing out of its back”, is a little-known creature restricted to the Likouala-aux-Herbes in the Congo.
It has only ever been seen in the water with only its back protruding, exposing large “planks” with algal growth between them. What it looks like underwater remains unknown. The mbielu-mbielu-mbielu does not show any aggressive behavior and is presumably herbivorous.
The suggestion that it is a late-surviving stegosaur is dubious at best, considering that stegosaurs went extinct long before the end of the Cretaceous (with the possible exception of the disputable Dravidosaurus).
Mackal, R. (1987) A living dinosaur? E. J. Brill, New York.
Weishampel, D. B.; Dodson, P.; and Osmolska, H. (2004) The Dinosauria, 2nd Edition. University of California Press, Berkeley.