Twilight Arrowhead

Evolving rather closely alongside its surface dwelling cousin, the twilight arrowhead features much of the same internal features and anatomy save for several differences. Unlike its cousin, it has a thicker, stronger exoskeleton, though its endoskeleton is less dense as a result. They have evolved a small internal organ capable of producing clicks which it uses to navigate via a weak form of sonar alongside its ability to "see" the bioelectric byproduct produced by all living things.

Adults have small patches along their sides where they can form small bioelectric currents and "flashes" so that they may more effectively communicate with one another. They are not as powerful a swimmer as their surface cousins, but they have fewer predators so it is not as necessary.