Sponges and Coelenterates respire through-------------------.

Sponges and Coelenterates are simple multicellular organisms that lack specialized respiratory organs.

In these organisms, the exchange of gases (oxygen and carbon dioxide) occurs through simple diffusion across their entire body surface, which is essentially the plasma membrane of their cells.

Book gills are found in horseshoe crabs, book lungs in arachnids, and cloacal respiration is seen in some aquatic animals like sea cucumbers and certain turtles.

Answer: Plasma membrane