Castiarina allensundholmi is a species of beetle in the family Buprestidae, otherwise known as jewel beetles. The species was discovered in October 2003 and was described by Dr Shelley Barker, OAM (Medal of the Order of Australia), in 2005. The three specimens in the type series measure from 7 mm to 8.2 mm. The species belongs in the Castiarina balteata species group which currently comprises three similarly-sized described species: Castiarina balteata (Saunders, 1869), Castiarina williamsi (Barker, 1988), and Castiarina allensundholmi Barker, 2005.