Arrowheads

On Sagan IV, the word arrowhead is used to describe a group of worm-like organisms with crustacean-like characteristics that are members of the kingdom Cillognathias. They originated from a tiny, green, worm-like creature, but then they diverged into more diverse armored forms.

Anatomy


The arrowheads have a diverse range of forms, ranging free-swimming predatory speartongues to the bottom-dwelling muckrakers. They all share a duel brain system, with the upper one controlling movement and its active actions such as feeding while its lower brain performs passive actions such as breathing and bodily functions. They also all possess a soft, spongy organ located just behind their head that allows them to "see" the bioelectric byproduct produced by all living things. Finally, all the descendants of the twilight arrowhead possess an organ capable of producing clicks that are used for sonar and have small patches along their sides where they can form small bioelectric currents and "flashes" in order to communicate with one another

Breathing and Blood
Arrowheads have colbalt based blood (coboglobins). When without oxygen it appears yellow but when exposed to oxygen it appears pink.