Die stickstoffhaltigen stoffwechselendprodukte und ihre exkretion bei Paracentrotus lividus

The perivisceral fluid of Paracentrotus lividus (Lamarck) contains, as main end-products of the nitrogenous metabolism, ammonia, urea, creatine, creatinine and traces of uric acid. In the organs analysed, the distribution and abundance of ammonia and urea fluctuate considerably. the intestine was found to have the highest NH₄ ⁺?N and the lowest urea-N contents. The axial organ contained the highest amount of urea-N and the lowest quantity of NH₄ ⁺?N; the perivisceral fluid, including the coelomocytes, contained intermediate amounts. The special relations to hemal system and coelothel, the presence of excretory material, and the analogous conditions to other invertebrates, suggest that the coelomocytes and parts of the intestine and axial organ are excretophoric and able to synthesize urea. From the known distribution of ammonia and urea in echinoid species, it is concluded that the ability to synthesize urea must have developed and improved in efficiency during echinoid evolution. P. lividus is predominantly ureotelic. It excretes approximately 91% of the nitrogenous wastes released into the surrounding sea water as urea-N, and only 9% as ammonia-N. Ammonia, and most of the urea, are excreted via the body surface — probably through respiratory surfaces; however, one third of the urea is excreted through the intestine, since urea excretion decreases by this amount when the anus is sealed artificially.