Cephalasips

Cephalaspis was a prehistoric jawless fish the size of a modern trout.

Facts
Cephalaspis was a member of the Osteostraci, one of the most advanced sorts of Palæozoic armored jawless fish. They were scavengers and bottom-feeder, unable to bite, instead feeding on worms, algae, and small shellfish on the sea-floor by sucking them into their jawless mouths utilizing water pressure; they would have also been prey for the large arthropods of her time, including the thunder-scorpion Brontoscorpio and sea "scorpions" (i.e., eurypterids). They lived during the late Silurian period, roughly 400 MYA.

To escape from being eaten, these fish had evolved an early warning system: special sensors on their skin detected even the tiniest vibrations in the water - it would become the lateral line system in the modern fish. But when Cephalaspis detected danger and were already swimming away from it, with their defensive headgear, they couldn't swim fast for long. They had to rest frequently, or they'd tire completely very quickly.

When breeding season came, Cephalaspis congregated to head for the one place they could escape the scorpions: fresh water, inland, with their convoy plowing upriver, away from the sea. They returned to the spawning grounds where they hatched, using memory. Their toughened head had a vital weapon, one of the first complex brains, which is much more developed than their rivals who had no memory at all. This brain allowed Cephalaspis and other early vertebrates to process the information surrounding them that they received from their senses (and the lateral line system) and to escape from dangerous predators, such as the giant Pterygotus.

In the Koba Files Series
They make their appearance in the Koba Files Series. They appeared in a few pet stores. They were also farmed for food. They were mostly list as an endangered species: due to habitat loss, pollution, invasive species, & culling. They were mostly sea creatures, but would swim to freshwater sources to breed. Which became a problem: since there was overfishing going on, they populations started to decrease. Their eggs were often taken & illegally sold for food: which they cost a lot of money (at least $100). Despite that scientists started capturing them & captive breed them. They then were later sold to pet stores: so fish hobbyists would often keep them & breed

With the Creature Protection Team, they purchase some of the fish for research. They put them in a special enclosure for them: it was half saltwater, half freshwater. The enclosure had a smooth man-made muddy wall, the saltwater part a coral reef & kelp forests, the freshwater part was form as a man-made pond where it has some mud & small plants around it. It also had a second floor for visitors who want to view them from above.