Nephridia, also known as excretory tubules, are specialized structures involved in the process of osmoregulation and excretion. They are lined with ciliated cells and contain channels or ducts that connect the internal body fluids with the external environment. The nephridia filter waste products, such as nitrogenous compounds and excess water, from the body fluids and transport them to the nephridopores for release.
The number and arrangement of nephridia and nephridiopores can vary among different invertebrate groups. In flatworms, for example, there are typically multiple pairs of protonephridia, each ending in a nephridiopore. In earthworms and other segmented worms, nephridia are arranged in a segmental pattern, and each segment has a pair of nephridiopores.
The presence and functioning of nephridia and nephridiopores play a critical role in maintaining the internal water and solute balance of the organism, ensuring the proper functioning of various physiological processes.