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(invertebrate zoology)
Any of various paired excretory structures present in the Platyhelminthes, Rotifera, Rhynchocoela, Acanthocephala, Priapuloidea, Entoprocta, Gastrotricha, Kinorhyncha, Cephalochorda, and some Archiannelida and Polychaeta.



an excretory organ that is characteristic of invertebrates. The nephridium regulates osmotic pressure, extracts and removes harmful metabolites from the body, and sometimes transports gonad products. The most primitive nephridia are those of flatworms, rotifers, gastrotrichs, nemerteans, and some polychaetes. These nephridia, which are called protonephridia, are branched tubules of ectodermal origin. They are closed at the internal ends by terminal cells, or solenocytes, and open to the exterior by means of excretory pores, or nephridiopores. Upon losing its solenocytes and opening into the coelom, the protonephridium is transformed into a metanephridium (primarily in annelids). In some annelids the nephridium coalesces with the mesodermal ciliated gonad funnels, or coelomo-ducts, forming an organ of mixed origin, the nephromyxium.


References in periodicals archive ?
Nephridial tubercle free from third and fourth pads, in lateral posterior position.
602) drew attention to the characteristic absence of nephridial pores in Tritogenia.
Nephridial bladders were previously termed 'caeca' by me, following Brinkhurst and Jamieson (1971: 57-60).
Excretory system holoic; one pair of nephridia per segment (except for three anterior segments); large or medium-sized, tightly coiled loops with elongated nephridial bladders, V-shaped or J-shaped at the ectal end.
2 Holandric or metandric (male funnels in 10 and 11, or only in 11); dorsal blood vessel simple throughout the whole body length; excretory system holoic with J-shaped nephridial bladders.
Holandric (male funnels in 10 and 11); dorsal blood vessel double in certain preclitellar segments, simple when crossing septa; excretory system holoic, with large or medium-sized, tightly coiled loops and elongated, V-shaped nephridial bladders 3
3 Coiled nephridial loops bushy, very large, V-shaped nephridial bladders widely open.
1, 8) and four complete creeping pads with nephridial tubercle opening between the 3rd and 4th pad (Figs.
The position of the nephridial tubercle on the fourth and fifth foot distinguishes P.
Spermathecal pores: In intersegmental furrows 13/14, 14/15, 15/16, numerous, 9-14 on each side, begin around the line of nephridial pores and scattered until mid-dorsal line.