In arthropods the respiratory system is open (lacunar). Blood, also known as hemolymph, is pumped by a heart and falls into cavities (lacunas) irrigating and draining tissues.
All arthropods have a heart. Crustaceans and arachnids have respiratory pigments. Insects do not have respiratory pigments since their blood does not carry gases (in them gases reach tissues and cells through tracheal structures).