. The biology of marine animals. Marine animals; Physiology, Comparative. 44 THE BIOLOGY OF MARINE ANIMALS the secretion of water. It is interesting, in this regard, that the nephridial canal of N. diversicolor is longer and more convoluted than that of P. cultrifera, suggesting nephridial participation in osmoregulation. Isolated tissues of N. diversicolor continue to function in low dilutions, and display spontaneous activity in 5-10% sea water. In P. cultrifera, on the other hand, the lower limits of salinity that will still permit muscular activity lie between 20-25 % sea water (144). A se
. The biology of marine animals. Marine animals; Physiology, Comparative. 44 THE BIOLOGY OF MARINE ANIMALS the secretion of water. It is interesting, in this regard, that the nephridial canal of N. diversicolor is longer and more convoluted than that of P. cultrifera, suggesting nephridial participation in osmoregulation. Isolated tissues of N. diversicolor continue to function in low dilutions, and display spontaneous activity in 5-10% sea water. In P. cultrifera, on the other hand, the lower limits of salinity that will still permit muscular activity lie between 20-25 % sea water (144). A seemingly racial difference has been described in the osmoregulatory performance of N. diversicolor. Animals at Bangor and Plymouth require more than 100 hours to complete their weight regulation in 20% -to ."a C o Co. Time (hours) Fig. Osmotic Adjustment in Nereis diversicolor Salt loss accompanying water intake in dilute sea water (concentrations shown against each curve). (From Ellis, 1937.) sea water, whereas worms at Roscofftake only half that time (Fig. ). Racial differences of this kind might be expected to develop in animals inhabiting waters of low salinity, as adaptations to new or altered environ- mental conditions. Freshwater molluscs have well-developed osmoregulatory powers, and this rather suggests that brackish-water forms may be able to regulate their internal media. The bivalve Mercenaria mercenaria shows some hyper- tonicity in dilute sea water (blood 374 mM CI, in sea water 319 mM CI). Potamopyrgus jenkinsi', sl brackish-water gastropod, has invaded fresh water in recent historic times. On the other hand, certain freshwater pulmonates have penetrated into brackish waters, Limnaea pereger, and several species are found near high-tide mark on the shore. Littoral prosobranchs. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrat
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