Achaeus spinosus

Achaeus spinosus
Decorator crab (Achaeus spinosus) covered in hydropolypes on Ianthella basta (elephant ear sponge). This crab is using hydropolypes to cover its shell in order to provide protection from predators. The crab benefits from the hydropolype's sting while the hydropolypes benefit from the crab's mobility allowing it to feed in a larger area.
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Family: Inachidae
Genus: Achaeus
Species:
A. spinosus
Binomial name
Achaeus spinosus
Miers, 1879 

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