This deep-sea fish's tubular eyes rotate inside its own transparent, fluid-filled head
The barreleye fish, Macropinna microstoma, has a dome of clear, fluid-filled tissue covering its head, through which its barrel-shaped, tube-like eyes are visible. For decades scientists assumed those eyes were fixed pointing straight up, to spot prey silhouetted against faint sunlight from above. In 2008, researchers using deep-sea cameras finally filmed a live barreleye and found its eyes can rotate forward within the shield, letting it watch food it's about to eat without turning its body.