Water Compartments and Osmoregulation in the Parasitic Nematode Pseudoterranova Decipiens Available to Purchase

A study of the time course of penetration of ³H₂O into whole worms suggests that worms immersed in a hypo-osmotic environment (15% artificial sea water) reach full exchange equilibrium more slowly than worms in an iso-osmotic environment (40 % artificial sea water). The apparent water content, determined by dry mass, matches that determined by ³H₂O exchange when worms are immersed for 24h in 40% artificial sea water (ASW), but the water content measured by ³H₂O exchange is lower when worms are kept in a hypo-osmotic environment for 24h. These differences disappear after 48h. No such differences are apparent when sacs, consisting of cylinders of body wall lacking their intestines and pseudocoelomic fluid and closed at both ends by ligatures, are immersed in either 40% or 15% ASW for 24h. The placing of ligatures at the head, but not at the tail, results in a failure of worms immersed in 40% ASW or 15% ASW containing ³H₂O to achieve full exchange equilibrium within 24h. These results suggest that although worms immersed in an iso-osmotic environment drink, those immersed in a hypo-osmotic environment do not, a conclusion supported by studies involving the addition of [¹⁴C]inulin to the medium. The application of ligatures to the head and tail of worms immersed in 40% ASW results in a slower penetration of ³H₂O into the pseudocoelomic fluid, whereas similar ligatures do not further retard the penetration in worms exposed to 15% ASW. The results are consistent with a model which sees the pseudocoelomic fluid as consisting of two compartments containing water, one of which exchanges more slowly than the other.