Hemolymph ion composition and volume changes in the supralittoral isopod Ligia pallasii Brandt, during molt

We analyzed ion composition and volume of the hemolymph of Ligia pallasii i n four different stages of the molt cycle using capillary electrophoresis a nd H-3-inulin. The main ions in the hemolymph were Na+, K+, Mg2+, Ca2+, and Cl-. The Ca2+ concentration increased significantly during the molt by 47% from intermolt to intramolt and by 37% from intermolt to postmolt, probabl y due to resorption of Ca2+ from the cuticle and sternal CaCO3 deposits. Th e K+ concentration increased significantly by 20% during molt. The hemolymp h volume normalized to the dry mass of the animals decreased by 36% from in termolt to late premolt. This was due to a reduction in the hemolymph volum e and to an increase in dry mass of the animals during premolt. A sudden in crease in the hemolymph volume occurring between late premolt and intramolt served to expand the cuticle. Since the Na+, K+, Mg2+, and Cl- concentrati ons did not change significantly from late premolt to intramolt, the increa se in hemolymph volume suggests an uptake of seawater rather than freshwate r.