Dartfin

The dartfin split from its ancestor, the ovi gillfin. Since Ovi Temperate Salt Lake was an isolated habitat in early Masonian period, it couldn't migrate to other habitats. It has specialized in feeding on lacrimucks because other food was already consumed by other specialists. For feeding on the soft flesh of lackrimucks, the dartfin has evolved scissor-like beaks and interleaving jaw-fronts, which are also acting like a scissor. With these jaws it could easily cut out pieces of flesh out of the base of the lacrimucks, or eat the sweet and nutritious bubbles at the end of the branches. For better escape from predators like the rhopa and the speartooth seaswimmer it forms small swarms.

Since their ancestors were hunted by the rhopas, the dartfin has got faster to escape the rhopas. The dartfin has evolved a sleek, body and a big tail fin for swimming with up to 70 km/h. For stabilizing itself at that speed, the dartfin has two strong stabilizer fins. It also has evolved stiffeners in its tail fin for better swimming and in the vertical fins for better turning at that speed. The eyes have lost their eyestalks and merged into the head for not slowing down when swimming fast.

When swimming fast, the dartfin can retract the gilled front backing of the dorsal fin. When retracted, the front backing lies closely to the body, which causes the dorsal fin to drift around loosely. The retraction of the front backing has the handicap that the dartfin can only breathe hardly. For not to not suffocate the dartfin has to pop up the gilled fin-backup and swim relatively slow after a couple of seconds to be able to breathe.