Carrier Crab are from the family of Homolidae, but not sure which species/genus this one is. They are known as Carrier Crab or Porter Crab as they carries other animals such as Upside-down Jellyfish and Sea Urchins on their back as a defence mechanism. The Up-side down Jellyfish is from the genus Cassiopea.
Seen during a night dive. The crab hides in the sandy bottom during day time and come out to feed at night time.