Agnatha are ectothermic, also known as cold-blooded. This means they rely on external sources of heat to regulate their body temperature.

Here's why:

* Lack of internal heat generation: Agnatha, like fish, lack the physiological mechanisms (like fur or feathers) to generate their own internal heat.

* Environment dependent: Their body temperature fluctuates with the surrounding environment. They become warmer in warmer water and colder in cooler water.

Therefore, Agnatha, including lampreys and hagfish, are not endothermic.