Water uptake via two pairs of specialized legs in Ligia exotica (Crustacea, Isopoda)

When individuals of Ligia exotica were exposed to dry environments, their weight decreased within 3 h to 90% of the initial weight. When the animals were subsequently presented with wet paper, pereiopods VI and VII were firmly apposed and moved around until their tips were stationary for some seconds. Subsequently the pleopods became soaked in water and the body weight recovered. Morphological observations revealed hollow structures on the surface of the dactylus and propodus of pereiopods VI and VII, and a series of thin cuticular protrusions, oriented in several parallel lines, from the propodite to the ischiopodite of pereiopod VI and on the basipodite of pereiopod VII. The width between the parallel lines varied little, but the total width of the regular lines increased linearly with increasing body size. When isolated caudal pereiopods were immersed, beginning at the distal end, in water, water flowed along pereiopod VI as far as the proximal end of the ischiopodite, but water flow along pereiopod VII occurred only in conjunction with the basipodite. This means that water uptake with the legs requires both pereiopods VI and VII and can be achieved only when these legs are closely apposed.