Amphioctopus marginatus "coconut octopus"

Kingdom: Animalia

Phylum: Mollusca

Class: Cephalopoda

Order: Octopoda

Family: Octopodidae

Genus: Amphioctopus

Species: A. marginatus

Introduction:

The Amphioctopus marginatus is commonly known as the "veined octopus" or "coconut octopus". A typical Amphioctopus marginatus has a body that is approximately eight centimeters in length and arms which are approximately 15 centimeters. Members of this species are able to rapidly change their outside appearance into a wide variety of colors and patterns due to a system of reflective and pigment cells in the skin. These cells are neurally controlled. Uses for this trait include predator evasion and mate attraction. Amphioctopus marginatus is also recognized for possessing a learning capability that rivals and even surpasses that of some vertebrates. This is made apparent by the species’ use of tools. Often finding multiple ways in which to make use of the same object.

Habitat and Diet:

Considered a medium-sized cephalopod, Amphioctopus marginatus is a wide spread species. They have been found in almost all benthic regions of the Pacific and Indian Oceans, including Australia, South Africa, Japan, New Guinea, and India. The species mostly remains in waters no deeper than 183 meters (600 feet), staying close to sandy sea floors from which they dig out some of their prey. Among the burrowing crustaceans, the coconut octopus also preys upon small fish, crabs, and shrimp.

Although being carnivorous, the Amphioctopus marginatus has developed a behavior that often makes use of plant resources, and from which the species gets one of its common names, the Coconut Octopus. Dwelling in relatively shallow waters, sunken coconut shells can be common place. The octopuses select one of a suitable size and carry them for camouflage and protection. This behavior is paired with another unusual camouflage tactic. Coconut octopuses exhibit bipedal locomotion while carrying the shell with their head and remaining six tentacles hidden within it in order to mimic the appearance and motion of a drifting coconut shell. The shells are also used for and alternate mode of transportation, in that, the octopus will take two halves of the shell and enclose itself inside of them, then roll along the sea floor.

Complex Behavior:

Octopuses are solitary invertebrates however, this has not impeded their intelligence. The Amphioctopus marginatus is in fact, regarded as one of the most intelligent invertebrates known. This is in large part due to the species' capability for learning and problem solving. The coconut octopus uses its advanced eyesight and incredible dexterity to manipulate found objects to accomplish many different functions.

A study was conducted to analyze such uses of tools, defense methods, modes of locomotion, and breeding behaviors. Five Amphioctopus marginatus, three males and two females, were collected from the Indian ocean and placed into tanks for observation. Each tank had a substrate of sand from the sea floor along with an ample amount of familiar objects with which the octopuses could build and use as tools. The tanks were 120x60x60 cm and were covered with plexiglass lids to prevent the subjects from escaping. Observations were made over a period of six months.

locomotory patterns:

All subjects displayed the bipedal mode of locomotion known as stilt walking where two limbs are made rigid and used as legs to propel the animal forward. All of the six remaining limbs are used as camouflage. This behavior is significantly different from the species’ typical mode of locomotion which is described as as using all of its limbs in a sprawling formation and using its suckers to pull the body along the sea floor.

Outside of captivity, the Amphioctopus marginatus has been repeatedly documented to use several of its limbs as rigid “stilts” while carrying coconut shells on its underside to carry eggs and for protection.

Defence:

In its natural habitat, the primary mode of defense is avoidance. This is achieved by burying its entire body in the sand of the sea floor with the exception of its eyes. Amphioctopus marginatus also have chromatophores in their skin which allow them to shift the appearance of theirs body’s surface. In captivity, the most common defense mechanism displayed was fleeing quickly by use of jet propulsion. Specimens also swam away casually, buried themselves in sand, rapidly changed its skin color from dark to light, and even gathered rocks to protect its underside.

Use of Shells:

For much of history, the use of tools was believed to be the sole province of humanity. Then vertebrate species such as chimpanzees and other primates were observed using tools as well. Among invertebrate species, the coconut octopus is the most well documented to share this behavior. Amphioctopus marginatus is not relegated to coconut shells as their common name might imply. The shells of conch, and other crustaceans are also commonly used. The limiting factor in shell choice seems to be only size and sometime carrying capacity. The shells are used as baskets to transport eggs, mobile protection, stationary camouflage, and mobile crypsis.

Breeding Behavior:

Mating among Amphioctopus marginatus appears to be opportunistic due to the solitary lifestyle of the species. Like most octopuses, the male is only present during copulation and the female remains with her eggs until they hatch. After laying her eggs, the female aerates them regularly using water jets and waving motions with her arms. This also keeps micro organisms and other debris from accumulating on the brood. Unlike most other octopus species, Amphioctopus marginatus is not completely sessile when caring for its eggs. However, remaining in the same place still seems to be preferred. The female will not eat and will eventually die around the time that the eggs hatch.

Works sited:

Finn, Julian K., et al. “Defensive Tool Use in a Coconut-Carrying Octopus.” Current Biology, vol. 19, no. 23, 2009, doi:10.1016/j.cub.2009.10.052.

Sreeja, V. & A. Bijukumar (2013). Ethological studies of the Veined Octopus Amphioctopus marginatus (Taki) (Cephalopoda: Octopodidae) in captivity, Kerala, India. Journal of Threatened Taxa 5(10): 4492–4497; http://dx.doi.org/10.11609/JoTT.o3256.4492-7

Tyrone Lucon-Xiccato, Elia Gatto and Angelo Bisazza, Fish perform like mammals and birds in inhibitory motor control tasks, Scientific Reports, 7, 1, (2017).

Jana Dewenter, Peggy Gerullis, Alexander Hecker and Stefan Schuster, Archerfish use their shooting technique to produce adaptive underwater jets, The Journal of Experimental Biology, 220, 6, (1019), (2017).

Joacim Näslund and Jörgen I Johnsson, Environmental enrichment for fish in captive environments: effects of physical structures and substrates, Fish and Fisheries, 17, 1, (1-30), (2014).