Why the cockeyed squid has mismatched eyes

by   Profile Herbert   When 23rd February 2017
Histioteuthis heteropsis (Cockeyed squid) in the deep waters of Monterey Bay (c) MBARI 2012
Video frame grab
Histioteuthis heteropsis (Cockeyed squid) 570 meters below the surface of Monterey Bay (c) MBARI 2012
Histioteuthis heteropsis (Cockeyed squid) (c) Screenshot Video, MBARI
Close-up of the larger eye, with its yellow lens (c) Screenshot Video, MBARI

Researchers solve mystery after examining 25 years of video footage

The animals in the deep seas comprise some of the most mysterious
inhabitants of our oceans.

Case in point: a squid with eyes that are of
different sizes, aptly named the cockeyed squid (Histioteuthis

Also known as the strawberry squid, one of its eyes is large and
yellow, while the other eye is small and bluish. A related species,
Stigmatoteuthis dofleini, has a protruding eye on one side and a normal
eye on the other side.

Although these species were discovered more than a century ago,
biologists have long been puzzled over the reason of the asymmetrical
qualities of the two eyes. Now, after analysing 25 years' worth of
video footage of the squids taken at depths of 200 to 1,000 metres,
researchers have discovered the answer.

Their findings have been
recently published in the journal Philosophical Transactions of the
Royal Society B.

It seemed that the larger eye was always being directed upwards, while
the smaller eye was directed downwards, indicating that the eyes served
different functions.

The larger eye, with its yellow lens, allowed the
squid to detect prey against the dim down welling surface light, and
makes them easier to spot.

The smaller eye specialised in scanning for
bright bioluminescent fashes emitted by prey in the dark waters from

As such, the smaller size of the downward-directed eyes enables less
energy usage, thereby maximising the squid's “energy efficiency”.

Link to the study



Written by
Profile Herbert
When 23rd February 2017
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