An orangutan crab rests on some bubble coral. (Credit: L. Galko-Rundgren)

Orangutan crab a dedicated decorator

  • May 15, 2014

Its fuzzy orange outer shell gives this orangutan crab its name

Contributor
Bec Crew

Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.

MEET THE FUZZY LITTLE orangutan crab, sitting on his pretty white home made of bubbles.

Found in the tropical waters of the central Indo-Pacific region, including off the coast of Indonesia, the Philippines and Japan, the orangutan crab (Achaeus japonicas) is only small, with a carapace that measures just 2cm across.

From its eyestalks to the tips of its very long legs, it's covered in a rusty-red coat of fine hairs. This shaggy pelt earned the species its common name, derived from the Indonesian word oran hutan, meaning "forest person". If the orangutan is the forest person of the land, the orangutan crab is the forest person of the sea.

It belongs to the decorator crab family Inachidae, the members of which are famous for their compulsion to attach debris collected from the ocean floor, plus tiny plants, sedentary animals, shells and gravel to their hairs for camouflage.

Decorator crabs a dedicated bunch

Decorator crabs are very particular about their decorations. In 1940, British zoologist and camouflage expert, Hugh Bamford Cott, tested the dedication of another species of decorator crab, the great spider crab (Hyas araneus) of the Atlantic Ocean.

He moved a number of them from their homes off the coast of Britain to different locations, and each time they were set down, they redecorated themselves using local materials. Each crab adjusted its camouflage on the very first night of its relocation. One of them had even broken off the arms of a crinoid - a small, feathery creature that looks like a flower - and wrapped itself in them.

The orangutan crab might spend a lot of time covering itself in things to make it blend into its surroundings, but that doesn't stop it from spending most of its time on bright white backdrop of bubble coral (Plerogyra sinuosa).

This strange organism forms a mass of grape-sized, bubble-like structures that swell during the day to optimise the coral's intake of light. At night, the bubbles shrink, and the coral releases tentacles to capture food, at which point the orangutan will likely be wandering the sea floor in search of its own meals.