Seeing A Surplus : It has lots of long legs, sure but no shortage of eyes either :

Gulherma Gainett, then a biologist at the University of Wisconsin Madison, was looking through a microscope at the embryo of a daddy longlegs when he saw it - or, rather, saw them.

Daddy longlegs, the group of splendidly leggy arachnids also known as harvestmen, have been thought to have just two eyes.

But there on the animal's body, illuminated with fluorescent markers, were what looked like four more vestigial eyes.

In the Journal Current Biology, Dr. Gainett, now at Boston Children's Hospital, and his co-authors report that they believe they have discovered remnants in the harvestman species Phalangium opilio of what may have once been fully functional eyes in the arachnids' ancestors.

Though these vestigial eyes don't mature fully, they appear on the harvestmen's bodies as they develop, shaped by many of the same genes as the creatures' true eyes.

Arachnids include spiders, scorpions, harvestmen and other arthropods, and divining the relationships among this group of organisms is tricky.

To do so, researchers must draw on both genetic information from modern arachnids and fossils of those that have long since vanished.

Dr. Gainett used fluorescent tags to study the development of harvestman eyes. The tags were designed to stick to opsins, light-sensitive proteins that exist in the eyes across the animal kingdom.

Looking at the shapes traced by the tags, he matched the locations of the unexpected opsins on the harvestmen to approximately where extra eyes grow on spiders and horseshoe crabs.

{ Spiders typically have eight eyes, and horseshoe crabs have 10.}

These findings suggest that the neural architecture that handles the daddy longlegs' vision may be quite old. [ Veronique Greenwood ]


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