Final answer:
Chloride cells are found in both fish gills and cranial glands of seabirds and are crucial for osmoregulation in saltwater environments by maintaining water and electrolyte balance.
Step-by-step explanation:
The cells found in both fish gills and cranial glands of seabirds that help with water balance are known as chloride cells. These cells play a significant role in osmoregulation, particularly in saltwater environments where the balance of water and salts is crucial for the survival of marine organisms. Chloride cells aid in the excretion of excess salts in marine fish and seabirds, maintaining the necessary balance of electrolytes essential for their physiological functions.