The hagfish is a slime-emitting ocean-dweller that's remained unchanged for 300 million years--and it shows. It has a skull (but no spine), velvet smooth skin, and a terrifying pit of a mouth that ...

Most of a hagfish's brain is devoted to scent detection ... They have a notochord (a flexible cartilage-like structure that runs along their back) and a cartilaginous skull, and are the only animals ...