. The biology of marine animals. Marine animals; Physiology, Comparative. 42 THE BIOLOGY OF MARINE ANIMALS medium. In distilled water or in certain stream waters the animals die and disintegrate, and it has been demonstrated that this is due to absence of calcium in the external medium (Fig. ). In nature Procerodes has been found in streams with minimal calcium levels of 0-5 mg/L, where they are exposed to fresh water for as long as 5 days during neap tides (100). Much of the water that is taken up osmotically by Procerodes, when in dilute sea water, passes through the parenchyma to the en
. The biology of marine animals. Marine animals; Physiology, Comparative. 42 THE BIOLOGY OF MARINE ANIMALS medium. In distilled water or in certain stream waters the animals die and disintegrate, and it has been demonstrated that this is due to absence of calcium in the external medium (Fig. ). In nature Procerodes has been found in streams with minimal calcium levels of 0-5 mg/L, where they are exposed to fresh water for as long as 5 days during neap tides (100). Much of the water that is taken up osmotically by Procerodes, when in dilute sea water, passes through the parenchyma to the endoderm where it is stored in large vesicles. Contrary to expectation, these vacuoles do not discharge into the gut. In dilute sea water oxygen consumption is increased once the worms have attained a steady state, and swelling proceeds beyond normal when the animals are subjected to oxygen lack, or are poisoned with cyanide (100). Procerodes is probably isosmotic with sea water, and in dilute media the tissues at first become flooded with water. Calcium is believed to act by. 40 60 80 Time (minutes) Fig. Behaviour of Procerodes ulvae in Distilled Water Upper curve shows increase in volume; lower curve, loss of salts. Arrows indicate dissolution of ectoderm. (Somewhat diagrammatic. Smoothed curves based on a figure of Pantin's (100).) lowering the permeability of the body wall to water and salts, thereby reducing the inflow until regulatory mechanisms become effective, while excess water is stored in endodermal vesicles. In summary, active osmo- regulatory processes in Procerodes appear to involve: the secretion of water, by nephridia or through the body wall, against an osmotic gradient; maintenance of depressed ectodermal permeability; retention of water in endodermal vesicles having a low salt content. Polychaeta. As indicated above, the sublittoral nereid worms Nereis pelagica and Perinereis cultrifera adjust to low salt concentrations by dilution of the body fluids and
Size: 2420px × 1032px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectmarineanimals, booksubjectphysiology
