Tissue osmolarity of the New Zealand land flatworm (Arthurdendyus triangulatus)

Tissue fluid osmolarity of flatworms kept with moist bark was 243+/-4 S.E.M. mOsm kg(-1). Tissue fluid osmolarity of those kept with water-saturated tissue paper was 205+/-5 S.E.M. mOsm kg(-1). Flatworms placed in water of 300 and 400 mOsm kg(-1) lost weight. Those placed in water of 0, 100 and 200 mOsm kg(-1) gained weight. This suggests that body tissue fluids were approximately 260 mOsm kg(-1). Tissue fluids were slightly hyperosmotic in external media of 200, 300 and 400 mOsm kg(-1), and strongly hyperosmotic at 0 and 100 mOsm kg(-1). The highest measured value of tissue osmolarity was 457 mOsm kg(-1) from a specimen in a medium of 400 mOsm kg(-1). The lowest value was 145 mOsm kg(-1) from a specimen in pure water. Transverse sections of flatworms from different media concentrations suggest that fluids are absorbed into or removed from all tissues.