Air lacks the supportive density and moisturizing qualities of water. Lungs and insect tracheae are two variations. Lungs are the respiratory adaptation of most terrestrial vertebrates Lungs are highly vascularized invaginations of the body surface that are restricted to one location. The circulatory system must transport oxygen from the lungs to the rest of the body. Land snails use an internal mantle as a lung.
Spiders possess booklungs.
Form and Function of Mammalian Respiratory Systems Located in the thoracic cavity, mammalian lungs are enclosed in a sac consisting of two layers held together by the surface tension of fluid between the layers. Air entering the nostrils is filtered by hairs, warmed and moistened. Alveoli are lined with a thin layer of epithelium which serves as the respiratory surface.