Coconut Octopus

Kingdom: Animalia

Phylum: Mollusca

Class: Cephalopoda

Order: Octopoda

Genus: Amphioctopus

Species: A. marginatus

Introduction

Amphioctopus marginatus, commonly known as the coconut or veined octopus, is a highly evolved cephalopod which is found in a wide variety of marine environments stretching from the Indian Ocean to the coast of Australia. As a benthic invertebrate, it spends much of its time on the open sandy environment of the ocean floor. Several behaviors seen in this species make it unique including a type of bipedal locomotion which individuals sometimes utilize while moving along the ocean bottom and its use of coconut shells and other similar structures as a shelter on the open sea floor.

Reproduction and Development

The coconut octopus is exclusively gonochoric and eggs are cared for by the female parent. Since females have been known to eat males of their same species, mating can be rather risky for male individual. As an adaptation to this behavior, males often disguise themselves as females in order to mate and survive. After fertilization, females will lay thousands of tiny (about 6mm in diameter) eggs connected as festoons and hold them close to her aboral side throughout the brooding period. The eggs require constant aeration, which the mother provides by beating the water with her tentacles. Since the eggs require this constant care, the mother octopus will stop eating and spend all of her time caring for her eggs which then leads to her death due to starvation.

Planktonic larvae emerge from the eggs after hatching and are carried away by sea currents. By the age of one to two years, these individuals reach sexual maturity and are ready to mate. These octopuses grow to about 8cm long (15cm including the tentacles) and live from three to five years.

Tool Use

In the past, tool use was thought to be unique to humans, but as more species have been studied, tool use has been seen in many other vertebrate animals as well. However, the coconut octopus is the first invertebrate animal to be studied which displays such behavior.

A tool is defined as something which provides no benefit until it is used for a certain purpose. This is seen in the coconut octopus when it utilizes coconut and gastropod shells as shelters in their environment. Individuals of this species will carry these structures around with them, putting themselves in danger in the process, so they can use them as a shelter in the future. This behavior likely evolved by individuals utilizing large bivalve shells as shelters. However, as coconut shells have become more abundant on the ocean bottom from humans discarding them, these octopuses have adapted to the abundance of these structures. Not only does this behavior show that these individuals are able to plan ahead, it also requires a high level of coordination and brain function to assemble two halves of a coconut shell into a functional shelter.

Locomotion

This species utilizes several types of locomotion to move about their environment. Like most octopuses, jet propulsion is a common form of movement seen in this species and allows them to quickly move about their environment. They also display “normal” crawling, using the suckers on their tentacles to push and pull themselves along the ocean floor. However, along with these normal octopod forms of movement, the coconut octopus also shows unique forms of locomotions such as bipedal movement and stilt walking.

Bipedal movement is extremely unique in octopods, with only this species and Adopus aculeatus showing this behavior. In this form of locomotion, the octopus usually wraps six of its arms around its body to provide camouflage while the back most pair are used as legs. It then walks along the ocean floor, utilizing only these two legs to move about its environment.

The other unique type of motion seen in this species is stilt walking. This is utilized when an individual is transporting coconut shells to be used in a new location. It is a very costly form of locomotion as it exposes the individual to predators and is much slower than any other form of movement that this species uses. However, this behavior is another piece of evidence to suggest that the use of coconut shells is distinctive tool use, as it requires the octopus to plan ahead and risk the cost of slower and more unprotected movement for the benefit of safety in the future.

Defense

As mentioned previously, the coconut octopus has many tools that it can use to avoid predation. Not only by physically hiding in coconut shells that they assemble to form a shelter, but through other forms of defense commonly seen in other octopus species. These defenses include camouflage utilizing the chromatophores in their skin and squeezing into small crevices available in their environment. They also show simple flight by swimming or burial in the soft sediments of the ocean bottom as well as jet propulsions to quickly get away from predators. The major predators that these octopuses are avoiding include the great white shark, viperfish, and larger octopuses. These defensive behaviors can also be utilized to capture their own food. As carnivorous predators, coconut octopuses often eat small fish, crustaceans, and shrimp on the ocean floor. Overall, this species of octopus has many unique adaptations to its environment and remains an incredibly interesting species to study.