Permeability of the integument of the horseshoe crab,Limulus polyphemus, to water, sodium, and bromide

✍ Scribed by Dunson, William A.

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 583 KB
• Volume: 230
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402300319

✦ Synopsis

Mean water movements across the double chitin membrane of the Limulus gill are 5,000-7,000 pmoles/cm2.h. The carapace is much less permeable to water than the gill; this difference is probably due primarily to the greater thickness of the carapace. Variations in serum sodium concentration due to salinity changes do not affect the rates of water diffusion across the gills or carapace. The cause of a substantial variation between individuals in integumental water permeability i s unknown. The sodium influx across the carapace of Limulus (0.7-1.6 pmoles/cm2*h) is only a fraction that of the unidirectional water flux under the same conditions (0.5 M NaCl on both sides). This difference may be attributed to the greater size of the sodium ion in solution. There is no apparent effect of variations in carapace thickness on the sodium influx. The double chitin gill membrane is similarly low in sodium and bromide permeability (about 0.5-0.6 pmole/cm2. h). Thus it appears that the gills may have a relatively passive role in ionic regulation. Their low rates of ionic diffusion help to restrict the loss or intake of salts as the salinity changes. However, the high gill permeability to water must pose a severe problem for an animal coping with changes in external salinity.