Mimic Octopus

This day-active octopus forages on sand substrates in full view of fish predators (like the golden trevally, Gnathodon speciosus); however, little is known about the specific predators of this octopus species. To confuse predators, this species has a few tricks up its sleeve [arms]. It forages by crawling along the soft bottom in drab brown colors to match its surrounding muck environment.

The mimic octopus, along with other long-armed species, uses its arm tips to probe down holes and flares its web to trap prey. In addition to these typical speculative foraging behaviors, individuals have been observed to forage through subterranean tunnels. An octopus would enter a tunnel completely and emerge from another hole up to 1 m (3 ft) from the entrance point!

When using jet propulsion to move faster, this species positions its arms to attain a flatfish shape and uses swimming behaviors similar to those of a flatfish (swimming durations, swimming speeds, and undulating body movements). In combination with a drab color, this octopus mimics non-toxic flounders and soles that a predatory fish may pass-up because they are difficult to eat. This flatfish swimming mimicry has also been described for other sand-dwelling species including Indo-Pacific White V octopus/ “blandopus”, Hawaiian Long-armed Sand Octopus, and the Atlantic longarm mimic octopus (Macrotritopus defilippi).

Unlike the other species, which remain camouflaged during flatfish swimming, the mimic octopus has also been reported to mimic visually conspicuous toxic animals through a high-contrast body pattern (dark brown and light cream) and postures or behaviors. Through flatfish swimming and high-contrast pattern, the mimic imitates the toxic flatflish (Pardachirus pavoninus and Zebrias spp.)

This species has also been observed swimming just above the sea-floor with arms trailing from the body, mimicking a poisonous lionfish (Pterios spp) with banded arms. To scare-off fishes, such as territorial damselfishes (Amphiprion spp.), the mimic octopus threaded six arms down its hole and raised two banded, curled and undulated arms in opposite directions. This mimicked the appearance of the venomous banded sea-snake (Laticauda sp.)

It is still unknown if the mimic octopus is actually toxic or bluffing. However, a flounder was observed trying to eat a mimic octopus and rejected it, which may suggests this octopus is unpalatable. Alternatively, this high-contrast body pattern may not be a “warning signal” but act as a disruptive pattern to break up the outline of the octopus’s body and inhibit visual predators to detect it.

Other distinct postures and behaviors have been observed and are open to interpretation. The mimic octopus was also observed sitting on top of sand mounds and raising all its arms above the body, each arm being held in a zigzag form. This may imitate large sand anemones (such as Megalactis spp.) that have stinging cells (cnidocytes).

A large female mimic octopus (arm span 600 mm or 2 ft!) was spotted swimming to the surface from 4 m (13 ft) deep. Once at the surface, the octopus slowly sank while undulating its arms. This behavior may be mistaken for jellyfishes that are found in the area.