Respiratory faculties of aquatic invertebrates

This chapter introduces the ‘who has what’ in terms of respiratory organs for major water-breathing invertebrate groups. It begins with sponges and cnidarians—groups that have no recognizable respiratory faculty—and continues through the bilaterian lineage, pointing out how bits and pieces of a respiratory faculty accumulate. The most complex respiratory faculties are found in molluscs and arthropods, which consequently make up the bulk of this chapter. Aside from the ancestral aquatic respiration, this chapter furthermore explains how also within some terrestrial (air-breathing) groups such as arachnids and insects, mechanisms that allow lone—even permanent—stays under water have secondarily arisen.