Why Does This Squid Have Asymmetrical Eyes?

Cock-eyed squid. Photo by Emily Simpson.
Cock-eyed squid. Image: Emily Simpson.

The deep ocean is filled with bizarre critters, and we’re still discovering new ones in the inky abyss. Yet, some of the most mysterious species have been known to science for quite some time. Case in point: the cock-eyed squid (Histioteuthis heteropsis), which was discovered in 1913.

Unlike most squid, the cock-eyed squid (also known as the strawberry squid) has unusual asymmetrical eyes. One eye is small and blue; the other gigantic and green. This unusual mismatch baffled scientists for over 100 years — until now.

Kate Thomas, a biologist and graduate student at Duke University, sifted through 30 years of cock-eyed squid footage collected by Monterrey Bay Aquarium Research Institute’s (MBARI) remotely operated vehicles (ROVs) to gather more information on these mystifying cephalopods. After viewing hours of footage, she discovered a trend: cock-eyed squid swim nearly vertically with their bodies slightly tilted. In this position, their small blue eye faces downwards, and their big green eye faces upwards.

The purpose of this swimming orientation is efficiency. The bigger eye looks up towards the surface, where it can collect sunlight and see predators and prey; the smaller eye looks down towards the abyss, where it can see the bioluminescent emissions of other deep sea creatures.

Normally residing at depths between 400 and 1200 meters (1312 and 3937 feet), cock-eyed squid migrate vertically at night. This means they travel up to waters near (if not at) the ocean’s surface to hunt for food.

The study’s senior author Sönke Johnsen said in a statement, “The eye looking down really only can look for bioluminescence.. There is no way it is able to pick out shapes against the ambient light. And once it is looking for bioluminescence, it doesn’t really need to be particularly big, so it can actually shrivel up a little bit over generations. But the eye looking up actually does benefit from getting a bit bigger.”

The ocean continues to amaze us. You can find the original article here.

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