The excretory organs of planaria are known as:

Explanation

Planaria the animals of the group of flatworms have a simple tubular excretory system called protonephridium. A protonephridium is a network of closed tubules without internal openings. The tubular system is spread throughout the body and branches are capped by a cellular setup termed as lame cell. Each lame cell has a tuft of cilia, whose beating propels interstitial fluid into the tubular system (The beating of cilia looks like a flickering lame, therefore these cells are termed lame cells). The tubular system is drained into excretory ducts, which open to the exterior through several nephridiopores (Fig. 15.7). Fresh water flatworms excrete very dilute urine. The parasitic flatworms, which are isotonic to the host environment, mainly function in disposing nitrogenous wastes.