Terrestrial oligochaetes demonstrate significant volume and osmoregulatory abilities that are under neurosecretory control. In the marine Oligochaeta, little is known of volume or osmoregulatory capacities. However, histological evidence has linked cerebral neurosecretion and osmoregulation. The present study investigates water, ion, and volume regulation in an intertidal oligochaete and the effects of ablation of primary neurosecretory centers (supraand subesophageal ganglia) on these parameters. Control, sham-operated, and ablated CZiteZZio arenarius were acutely transferred to diluted seawaters. Osmolality and Na, K, C1 (mEq/liter) concentrations were determined in total tissue water and in extracellular fluids. Extracellular volume was determined (using micropuncture techniques) as the fraction of the total tissue water in which 14C-polyethylene glycol was distributed. With transfer to diluted seawater, all worms demonstrated hyperosmotic conformity. Tissue osmolality decreased in all animals at the same rate indicating no effect of ablation on integumental water permeability. Two phases of volume regulation were observed. In phase 1 (0-6 hours) osmolality decreased while water content (gm HzO/gm solute free dry weight = s.f.d.w.) increased both intra-and extracellularly. During this period, some volume regulation was accomplished in the control groups, particularly during the first 5 minutes, by the excretion of extracellular Na and C1 (kmoles/ gm s.f.d.w.1 which limited water gain. Ablated worms, reflecting less extracellular solute loss, gained more water than control groups. In phase 2 (6-18 hours) osmolality was constant, and all groups demonstrated a slow intra-(IC) and extracellular (EC) regulatory volume decrease. The solutes that accompanied volume loss were Na (EC), C1 (IC), and unmeasured solutes (IC). Reduction in intracellular solute content was the most significant loss occurring during this period with little difference among the groups tested. We hypothesize the primary effect of ablation is on extra-rather than intracellular volume regulation.Oligochaetes are abundant in terrestrial, freshwater, and marine environments. Terrestrial forms face the volume and osmoregulatory problems imposed by hydration during rainfall-flooding and by desiccation in air, or in soils of low moisture content. Considerable information is available on the ionic and osmotic relations of these organisms, in particular Lurnbricus terrestris. This species can hyperosmoregulate in pond water by the active uptake of Na and C1 ions (Maluf, '39; Ramsay, '49a; Kamemoto et al., '62; Dietz and Alvarado, '70; Dietz, '74). Adaptations to a hypoosmotic environment also include a decrease in integumental permeability to water and a low drinking rate (Dietz and Alvarado, '70; Carley, '75), production of a hypoosmotic urine (Bahl, '45; Ramsay, '49b) by recovery of Na in the distal tubule of the nephridium (BoroMra, '651, and further water excretion in the form of a dilute rectal fluid (Dietz and Alvarado, '70). Under de...
