Question

what is protonephrida

Answer 1

A protonephridium (proto = "first") is a network of dead-end tubules lacking internal openings found in the phyla Platyhelminthes, Nemertea, Rotifera and Chordata (lancelets). The ends are called flame cells (if ciliated) or solenocytes (if flagellated); they function in osmoregulation and ionoregulation, respectively.
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Answer 2

Protonephrida are made up of many flame cells. In the flame cells, there are cilia at the 'tips'.Proto means first. they function in osmoregulation and ionoregulation, respectively.