Complex sentence: Coralline algae are red algae in the Family Corallinaceae of the order Corallinales characterized by a thallus that is hard, as a result of calcareous deposits contained within the cell walls.
Split into simpler sentences: Coralline algae are red algae in the Family Corallinaceae of the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls.