The bottom swarmer split from its ancestor and now lives deeper in the river. It developed bioluminescence which it uses for attracting the opposite sex. Its eyes grew bigger but because the muddy river is impervious to light, the eyes themselves evolved to be pressure sensitive and detect water pressure changes around the swarmer. Because it has no predators, its body grew longer. Both sexes are very territorial and in the darkness and in the mating season they will release a subsonic noise to alert of their presence and their territory.