Water uptake and loss via the urosome in terrestrial talitrid amphipods (Crustacea: Amphipoda)

Abstract

The amount of exosomatic water in the ventral channel can be controlled by uptake and loss via the urosome in simplidactylate and cuspidactylate landhoppers, palustral talitrids and beachfleas, but not apparently by sandhoppers. Both water uptake and loss involve deliberate dabbing of the uropod tips (uropods 1 and 2 in simplidactylate landhoppers and palustral talitrids, uropod 3 in cuspidactylate landhoppers and beachfleas) on to a wet or dry substratum. Water flows rapidly into, or out of, the central channel via capillary spaces between the body parts. Transfer of water forward from the abdomen to thorax is apparently facilitated by the beating of the pleopods, or, in those species with highly reduced pleopods, by the elongate distal lobe of the peraeopod 6 gill, which lies between the bases of peraeopod 7 and the first abdominal epimeron. Water also pools beneath the telson and is taken into the gut by anal drinking in all the species observed. These observations suggest that landhoppers, beachfleas and palustral talitrids take up water from the substratum using a mechanism analogous to that used by the terrestrial oniscoid isopods. Sandhoppers probably do not use this mechanism, since the morphology of their urosome reflects the selective pressures of their sand-burrowing way of life.