How do gills differ among lobsters, isopods, amphipods, and krill?

Among malacostracan crustaceans, respiratory structures vary significantly based on their evolutionary adaptations and environmental needs.12

• Lobsters (Decapods): These possess gills arranged in three series near the bases of their thoracic limbs. These gills are protected within a branchial chamber beneath the carapace, and specialized appendages create currents to funnel oxygenated water over them.21
• Isopods: In these animals, the respiratory function has shifted to the abdominal appendages (pleopods), which are thin and flattened. Terrestrial isopods may also possess specialized invaginated structures called pseudotracheae for breathing air.21
• Amphipods: Their gills are typically simple sacs or plates that have migrated to the inner side of their legs. These structures are fanned by the pleopods within a ventral tunnel formed by the coxal plates.1
• Krill (Euphausiids): Unlike decapods, krill lack a carapace that covers the leg bases, meaning their single series of branched epipodial gills are fully exposed to the surrounding water.12

These variations reflect diverse strategies for gas exchange, ranging from protected chambers in decapods to exposed or abdominal-based systems in other groups.12