I recently wrote an article for Reef Tools about Trapeziid Acropora Crabs and Pocilloporid Guard Crabs. The article explains the physical and behavioral differences between Crabs of the genera Trapezia and Tetralia. The article also offers some tips on keeping Acropora Crabs in captivity.
This photo shows a captive Trapezia cymodoce in an Acropora secale.
Read a more detailed version here.