Achaeus spinosus is a small decapod which belongs to the large family of the Inachidae or the spider crabs.

The Achaeus spinosus carapace has an oval shape and does not exceed 4 centimetres or 1.6 inches in length.

This crab possesses long fine clawless legs, except the front pair which is smaller and bears chelae (pincers).

[3] Achaeus spinosus can be observed in the tropical waters of the Indo-west Pacific area, including the Red Sea.

[3] Achaeus spinosus feeds on plankton and suspended particles which it catches by climbing on the host with whom it's in association to expose itself to the current.