This sweet coral crustacean and wonderful little crab is considered a super-star of the crab world. As it resembles the large apes of Borneo and Sumatra. With a thick coat of orangey red or reddish brown coat of fine hairs covering its long arms and body, this small cryptic marine critter, the Orang-utan crab. It measures about 1 cm to 2 cm in size, it is a relative of the Spider and Decorative crabs. It was identified and described in 1839 and its scientific name is Achaeus japonicus belonging to the Inachidae family. Although the genus of this species is yet to be confirmed.
The Orang-utan crab is found throughout the Indo-Pacific waters from tropical Japan, Philippines, Indonesia to Western Australia on shallow rocky reefs from depth of 2 m up to 20 m. It lives in symbiosis with the Grape or Bubble coral Plerogyra sinosa. The small cryptic Orang-utan crab is often found hidden in this soft coral in which it lives. Feeding on passing planktons and gathering floating invertebrates or particles brought by the current.
It is found in most rocky shallow reefs in Manado Mainland, Bunaken, Siladen and Lembeh Straits dive sites. A very attractive marine critter, relatively easy to find and also photograph although it can be quite shy and would quickly hide itself in the tentacles of the Bubble or Grape coral and stay close to the tentacles.