The Loh Down On Science

Do five eyes see better than two?

Garm & Nilsson, Proc. Royal Soc. B, 2013

Fig. 1 (a) Linckia laevigata in its natural coral reef habitat at Akajima, Japan, where it feeds on detritus and algae. (b) As in other starfish species, the compound eye of L. laevigata is situated on the tip of each arm (arrowhead). It sits in the ambulaceral groove which continues to the top of the arm tip. (c) Lateral view of the compound eye, also called the optical cushion, which is sitting on the base of a modified tube foot. The eye has approximately 150 separate ommatidia with bright red screening pigment. (d) Frontal view of the compound eye showing its bilateral symmetry. (e) The tip of the arm seen from below. The view of the compound eye is obscured by a double row of modified black tube feet (arrow). (f) The arm tip seen straight from above. Note that the eye is again obscured from view by a modified black tube foot (arrow). (g) The compound eye (arrowhead) seen from 45° above horizontal in a freely behaving animal. When the animal is active, the modified black tube feet spread out to allow vision. (h) If the animal is disturbed, it closes the ambulaceral groove (broken line) at the arm tip and withdraws the modified tube feet. The compound eye is then completely covered, leaving the animal blind.

Can sea stars see stars?

This is Sandra Tsing Loh with the Loh Down on Science.

Most starfish have bug-like eyes at the tip of each arm.  They’re only good for detecting changes in light level.  Or so you’d hope! 

Enter Anders Garm from the University of Copenhagen.  He kidnapped starfish from reefs near Japan.  Then set them free.  But at different locations and distances from the reef.  He filmed their attempts to return home. 

Those placed twelve feet away?  They walked around in circles, never finding their way back.  At six feet?  Half got home, half didn’t.  But at just three feet?  Every single starfish made a beeline to the reef!  Yet when he repeated the three-foot test on a black, moonless night?  They all got lost.  This proved that they use vision, not say, smell, to navigate.  And this means that their eyes form true images.

Granted, lab tests reveal that they’re colorblind.  And see only fuzzy images and general shapes.

Put another way, they won’t see your tan line but will notice those love handles.  Snorkel at your own risk.

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