There are many adaptations to observe some gills of various designs like in the mayfly and the freshwater shrimp, air sacs carried by the water boatman and the water spider and physical adaptations similar to breathing tubes like the mosquito larvae which allow invertebrates to respire underwater. Smaller organisms such as the freshwater worms might not show visually obvious adaptations to gathering oxygen but their red colour can act as a trigger for looking at oxygen carrying chemicals.