Imagine a world much like ours, except our ape ancestors decided they liked the trees and never climbed down and decided to try out these 'tool' things. sapient apes never evolved. Instead a predominately aquatic race evolved (race with limited ability to go on land, such as just long enough to lay eggs, count for this question).
My question is what sort of aquatic species would be the most likely to develop sapience, and what forces would encourage and lead to that development? By sapience I include regular tool use and at least second generation tools (ie, they build tools who's sole job is to build better tools). Communication and basic language of some form should also existed.
What forces would encourage sapience to evolve, despite the caloric expense of it? how would tool use develop, in a land without traditional hands what would be the means of creating and manipulating tools (unless your answer is that the most likely species to develop sapience already has some hand-like features, such as otters).
How would your species adapt as it developed sapience to look/behave different from it's non-sapient ancestor?
This world must be very close to earth, but need not be exactly like earth. It's okay to hypothesis minor differences from our earth; however, the world should predominately look and feel like our planet earth, with most of the same creatures evolving in the same ways and the same habitats and biomes. However, it's perfectly acceptable, for example, to assume that a species split off from a common ancestor of modern animals thousands of generations ago and that species is the one that ultimately achieved sapience.
Any species that predominately lives in and utilizes water, and can not live long term on land, counts for this question. Fish, mammals, aquatic reptiles etc etc all count as potential sapient species.