1 Gobionellus oceanicus: Respiratory system Helena Rachel da Mota Araujo , Leticia Aguilar , and André Luis da Cruz Laboratory of Animal Physiology, Institute of Biology, Federal University of Bahia, Salvador, Bahia, Brazil Respiratory System Te gill lamellae of Gobionellus oceanicus are arranged in a regular pattern and are supported by primary filaments on all four gill arches. Te filaments are shorter in the ceratobranchial and ventral regions of each arch. Te filament surfaces showed protuberances and cavities. Te secondary lamellae were transversely and regularly arranged on the filaments from the proximal portion to the apex. A simple pavement epithelium composed of polygonal epithelial cells covered the gill lamellae supported internally with pillar cells. Erythrocytes were identified in blood vessels in both filaments and lamellae (Aguilar et al., 2019). Tis structure guarantees the acquisition of oxygen for aquatic breathing (Figures 1–7). However, in conditions of low water availability, the capillaries of the palate integument with their short distance of diffusion to oxygen have the potential to acquire atmospheric air and satisfy metabolic needs (Aguilar et al., 2019). Among Gobiidae, it is a matter of form and function relationship, as said, mudskippers are amphibious air breathers with epidermal capillaries, while G. oceanicus are facultative air breathers without epidermal vessels or capillaries, being the most likely gas exchangers in regions with the thinnest epidermis. Te knowledge of the potential respiratory surfaces of G. oceanicus can also be important for the understanding of the biology of the species in rivers and estuaries that suffer anthropic impacts (Araujo et al., 2019). Microscopic Anatomy of the Animals. Edited by Matthias Starck. Copyright © 2021 John Wiley & Sons, Inc. DOI: 10.1002/9781118158036.maa20190153