Putative stingray mimicry in the small ocellate octopus (Amphioctopus fangsiao) using false and true eyes

Benthic octopuses inhabiting shallow waters have excellent antipredator behaviour, including mimicry and camouflage to protect their vulnerable soft bodies. Moreover, many octopus species possess eyespots (false eyes), which are considered to be instrumental in startling predators. Here, we report another pattern of display of eyespots in combination with true eyes by octopus. Wild-caught adults and laboratory-raised juveniles of the small octopus ( Amphioctopus fangsiao ), which has eyespots adjacent to the true eyes and inhabit sandy and muddy areas, were observed under captive conditions. Both adult and juvenile octopuses exhibited two distinct patterns of display using eyespots in response to threats (observers). For the first pattern, octopuses displayed eyespots in combination with spreading the web between arms (pattern 1). Additionally, horizontal bars were displayed across true eyes and horizontally narrowed eyes (pupils) were integrated in the horizontal bars, presumably to conceal the true eyes while startling predators. For the second pattern, octopuses displayed eyespots with flattened disk-like shaped arms and web, and a pole-shaped mantle was elongated posterior (pattern 2). Additionally, true eyes were emphasised by fully opening the pupils in pattern 2. The posture shown in pattern 2 presumably resemble the sympatric stingray ( Hemitrygon akajei ). This posture was observed even in the laboratory-raised juveniles, suggesting that the mimetic behaviour may be independent to the experience of encountering stingray. Overall, our observations suggest that A. fangsiao eyespots are likely multifunctional: in some cases, they may startle predators, while in others, they may help individuals mimic more well-defended organisms.