Ammonia and urea excretion of the nemertean Procephalothrix simulus Iwata: effects of salinity, temperature, body weight and amputation

摘要

The total ammonia nitrogen (TAN) and urea nitrogen excretion of the nemertean Procephalothrix simulus Iwata was determined under different conditions. Both of its ammonia and urea excretion rates increased with the elevation of water temperature, and the relationship between the TAN excretion rate and water temperature could be described by TAN (μg N g~(-1)h~(-1))=20.510e~(0.071t) (R~2=0.943, F=83.47, P < 0.001). When the salinity was elevated from 10per thousand to 45per thousand, the ammonia excretion rate firstly increased and then decreased, with the peak value being obtained at 20per thousand. The urea excretion, however, showed a positive relationship with salinity. The whole animal TAN excretion increased with the increase of body weight [TAN (μg N h~(-1))=15.853 W~(0.65) (R~2=0.871, F=458.73, P < 0.001)], while the weight specific rate of TAN excretion was negatively related with body weight [TAN (μg N g~(-1) h~(-1)) = 15.858W~(-0.35) (R~2=0.661, F=132.55, P < 0.001)]. When worms were bisected, the anterior body fragments had lower and the posterior body fragments had higher TAN excretion rate, suggesting that most of the ammonia was not eliminated by the excretory organs in this nemertean species. Results also showed that the anterior body fragments were faster than the posterior body fragments in regaining the normal level of ammonia excretion.