When feather duster worms and barnacles pull in their feeding appendages, it’s a sign they have detected changes in light intensity or a moving shadow. It does not mean that they can tell whether you are having a good-hair day.
One red, light-sensitive eyespot at the end of each sea star arm distinguishes the difference between light and dark. The six-rayed star uses this information to forage at night and remain protected under rocks and ledges during the day. If the sea star has 24 arms, it will have 24 eyes!
The rims of a bell jelly’s medusa are lined with bright red photoreceptors. Bell jellies use their eyespots to help them find the darker bottom where they feed.
Invertebrates completely without sight are numerous—or at least I thought they were. But in the exciting world of marine biology there are new discoveries around every corner. Questions about marine invertebrate vision abound. If some supposedly sightless organism only spawns at night when it’s dark, how does it know it’s dark, if it can’t see? Answers to this question and others are leading researchers to take another look at sight in the ocean. Before long, all my old standby sightless animals—sea urchins, sea anemones, sea cucumbers, sponges, and tunicates—may well be declared photosensitive.
Perhaps, “To see or not to see?” is not the question after all. Perhaps, “To see well or to see just well enough?” is
a more appropriate question. Time and research will tell.
Oregon Coast March/April 2007