Eyes in Strange Places

Many marine creatures can see in all directions at once. Most fishes have eyes placed at opposite sides of their heads, permitting sight through a full sweep of 360 degrees. Other creatures, like the fiddler crab, have eyes on stalks, which can be moved about to extend their visual horizons.

The queen conch, a large, seagoing snail, has it eyes at the ends of two long tentacles. The more familiar land snail also has two hornlike tentacles which are somewhat light-sensitive and supplement the eyes at the base of its tentacles.

The way fishes’ eyes are placed–pointing up, down or sideways–depends on environment. The dlounder is an unusual case, however. It starts life swimming upright in the ordinary way, with an eye on either side of its head. But as the flounder grows, its body becomes round and flat, and it swims along the bottom on what formerly was its side. At the same time, one eye migrates to the other side of the head, so that the full-grown flounder has two upward-looking eyes.

Life Science Library - Light and Vision