Respiratory faculties of amphibious and terrestrial invertebrates

Abstract

This chapter focuses on the respiratory faculties of invertebrate air breathers. Although the partial pressure of oxygen in water is the same as in the surrounding atmosphere, the oxygen content per unit volume is around 30 times less due to its relatively low solubility in water. So it is no wonder that there is evidence for invertebrate animals on land as early as from the Palaeozoic. In spite of this apparent metabolic advantage, aside from some annelid groups, the only invertebrates to truly call dry land their home are some snails and arthropods. Among the latter, we see several independent origins of air breathing, and crustaceans present a particularly interesting study group in this regard. Arachnids and insects, on the other hand, were from the beginning terrestrial and air breathing, and insect tracheae form the most effective respiratory system going.