Octopus bimaculoides can learn to utilize a mirror to localize a reward outside the line of sight

Mirror-mediated localization of hidden objects is well documented in vertebrates^{1,2,3,4,5,6,7,8,9,10,11,12} but has never been demonstrated in invertebrates. Using mirrors to locate otherwise occluded objects is a form of mediated perception, linking a visible reflection to an occluded location^13,14 and is seen by some as a precursor to self-recognition.¹⁵ Cephalopods offer a fascinating test case of convergent cognition, having independently evolved sophisticated perceptual and cognitive abilities that are similar to mammals,^16,17,18 after diverging from a common ancestor over 520 million years ago.¹⁹ In addition, they react to mirror images as though they were conspecifics.^20,21,22,23 We projected a virtual crab that was visible only via mirror reflection onto a tank wall. Three Octopus bimaculoides were trained to navigate to the projection site instead of the mirror. All three octopuses learned this task, successfully choosing the correct side in 73% of trials. Critically, octopuses sometimes moved away from the visible reflection and climbed over the side walls of the start chamber to reach visually occluded locations that were spatially aligned with the reflected prey location. This behavior suggests (1) the ability to inhibit a direct approach to salient visual stimuli, and (2) a spatial representation that integrates mirror information with knowledge of 3D tank geometry. These findings extend mirror-use capabilities to invertebrates, demonstrating that cephalopods can employ mirror reflections for spatial navigation. The independent evolution of cognitive capacities underlying mirror use across diverse taxa suggests that common solutions may have evolved to solve spatial navigation challenges.