Sorry I know this is like the 10 billionth aquatic Posthuman, I promise there will be less monotony.

Conquistadors: (Descendants of the Sliders)

Not all hope was lost for the remnants of the sliders’ population. After their frozen lab rants disappeared, they took to the open seas. Some gave rise to Leopleurodon sized predators, others became gracile and dolphin-like. However it was a small clade of fish eating generalists with a flexible enough diet who would win the sapience lottery. Baring more resemblance to a plesiosaur than a human or penguin due to generations of life in the open sea. Tools could be held in an elongated appendage derived from their tongue. Formerly used to filter microbes out of the water for consumption. Despite their numerous newfound adaptations to the Alecia life, they were still capable of occasionally flopping themselves onto land, with their smooth skin being able to go a fair amount of time without drying out.

this gave them a leg up over the Tool Breeders as they had prober access ti metalwork and fire. Though progress was rather tedious up until true industrialization. In which they witness a massive surge in innovation of living near and exploring the terrestrial world. (WIP)