A xeno crab (Xenocarcinus tuberculatus or whip coral spider crab) and a ghost goby (Pleurosicya mossambica) hanging out. They are both typical whip coral critters that probably share a commensal or symbiotic relationship with the coral, but little is known about their relationships with their hosts.

A commensal relationship is one where one species benefits while the other is not harmed. Symbiosis is when both species benefit.