A long time ago, one of my “must have” species was Altolamprologus calvus. A physically unique cichlid from Lake Tanganyika, calvus are laterally compressed so they can get into rock crevices to both feed and breed. They also possess special flank scales that serve as a type of body armor. These fish will turn broadside where they are most protected to absorb attacks by predators and even conspecifics. These flank scale edges are quite sharp and can inflict damage on their own.