Lilliput Longarm Octopus

Macrotritopus defilippi, widely referred to as the Lilliput longarm octopus or Atlantic longarm octopus, is a diminutive species of marine cephalopod mollusk belonging to the order Octopoda. This species is distributed across the Atlantic Ocean, the Mediterranean Sea, and parts of the 🌊 Indian Ocean, predominantly inhabiting shallow sandy regions. The species employs a yellowish-brown coloration that facilitates effective camouflage within these environments, rendering it largely indistinguishable from its surroundings when motionless. Notably, in the Caribbean, it has been observed to mimic the swimming patterns of the plate fish (Bothus lunatus), a flounder species endemic to the same habitat.

Macrotritopus defilippi exhibits relatively long arms and a mantle length reaching up to 90 mm (3.5 inches). Similar to other octopus species, its skin demonstrates a high degree of color variability, often appearing plain or speckled to seamlessly blend with sand-dominated substrates. In regions where gravel is interspersed with sand, the skin may display a larger mottled pattern, and the octopus might develop small papillae and light and dark arm barring. A white leucophore located on the mantle tip may further contribute to disruptive camouflage effects in areas with white pebbles. The species' sophisticated ability to adapt its appearance to its surroundings makes it exceedingly challenging to detect when at rest on the seabed. Furthermore, the octopus is capable of concealing itself entirely beneath the substrate without leaving any visible indication of its presence.

The geographic distribution of Macrotritopus defilippi spans the Atlantic Ocean, including the 🌊 Caribbean Sea, the Mediterranean Sea, and extends to the northern 🌊 Indian Ocean and the coast of 🇸🇴 Somalia.

Despite its effective camouflage when stationary, the species is an active predator requiring mobility to forage. Camouflage is compromised during movement; however, Humann and DeLoach (2002) noted that Macrotritopus defilippi occasionally swims backward in a conventional octopus manner and, at times, advances in a flattened posture resembling a flatfish, with its arms trailing alongside. This mimicry is further enhanced as the octopus adheres closely to sand contours, thus avoiding shadow creation.

In the Caribbean, Macrotritopus defilippi shares its habitat with Bothus lunatus, a flounder that also exhibits variable coloring for substrate camouflage. When this flounder moves, it exhibits characteristic short burst swimming. Hanlon, Watson, and Barbosa (2010) have suggested that the octopus is an effective mimic of the flounder during such movements, exhibiting similarities in the duration and manner of swimming, and maintaining a similar posture. Typically, the flounder swims for approximately six seconds (range: 3-43 seconds) and rests for 2 to 3 seconds (range: 1-8 seconds), whereas the octopus swims for around two seconds (range: 1-20 seconds) and rests for 1 to 13 seconds. Both organisms maintain close proximity to the seabed's textured sandy contours, where the octopus' lifted eye placement enhances its resemblance to the lefteye flounder. Huffard's (2006) research hypothesized that mimicry of a fish might offer protective advantages, as potential predators are less inclined to attack what appears to be a robust flounder, seen as too large for consumption, unlike a vulnerable, soft-bodied octopus.

In the 🌊 Pacific Ocean, other octopus species such as Thaumoctopus mimicus are documented mimicking flounders, yet Macrotritopus defilippi remains the first known example from the Atlantic. Previously, unidentified larvae with notably long third arms were recognized in the Caribbean; however, their adult form remained unknown until a female was matured in a laboratory setting, revealing these as Macrotritopus defilippi larvae. These larvae display an extended-arm posture and, upon alarm, rapidly propel themselves by jetting, sometimes reaching the seabed to seek refuge. It is believed that they are pelagic nocturnally and benthic diurnally, although they appear to become less nocturnal with maturity.