Salt and water balance in the polychaete Nereis virens

1. 1. Nereis virens is a large and common estuarine and coastal nereid polychaete of the North Atlantic Ocean, frequently used in physiological experiments. 2. 2. N. virens is euryhaline, surviving from about 5% o (15% SW) to over 100% SW. 3. 3. N. virens is slightly hyperosmotic at all salinities, with a modest increment in coelomic fluid hyperosmoticity when adapted to salinities below 25% SW. 4. 4. There is only very limited hyperregulation of Na + and Cl + in worms adapted to low salinities; K + is strongly hyperionic at all salinities. 5. 5. pH of coelomic fluid increases as the salinity of the medium declines. 6. 6. Volume regulation is moderately well developed, but declines in animals maintained in salinities below 25% SW.