I'm forming a race for my fantasy world Eladine. The basic premise is that it is possible to go back and forth between our world and that one (almost like its another pool from the wood between the worlds in the Magician's Nephew, except that you don't get there that way). Almost no one knows about the existence of the other world(s?).
Anyway... the Dortoka.
Anatomy - Humanoid (partially) - half human, half sea turtle. They walk upright like men, though a little shorter (avg. 5ft tall). The lower half of their faces and their eyes are human; the upper half and nostrils are sea turtle. They have a shell on their back, and their upper torso is like the underbelly of a sea turtle. Their arms and legs are humanoid, but some have flippers in place of hands or feet. Males have long, narrow, dark colored shells (like a leatherback sea turtle), but females have round shells with beautiful patterns (like a loggerhead or hawksbill).
They live in/near the ocean, especially the Kaerim Isles. Each individual is different, but most spend their days swimming in the ocean hunting/enjoying themselves, and come to the shore at night to sleep. They mostly operate in small, fluid communities made up of singles, couples, and young ones.
They interact with other races (particularly humans) peacefully but with wariness. There is one city on their islands, which the dortoka wouldn't have built except for the trade between them and the mainland. The city is half populated by humans, and there is a council that is half dortoka and half human governing the city, but it has no authority on the rest of the islands. Humans are not wanted elsewhere on the isles.

That's pretty much all I've figured out. Please ask questions and point out any inconsistencies- anything to get my brain working and flesh these characters out!

Neat race. What do they eat? What do they trade with other races?

Very cool and unique! How do they walk upright if they have flippers, and what causes some dortoka to have flippers and others to have hands and feet? Is their underbelly as vulnerable as a normal turtle's underbelly? And how does having the shell help them?

They had mouths and digestive systems like humans. They eat kelp, fish, and other seafood (sometimes raw, sometimes cooked).
There are plants and metals that can only be found on the Kaerim Isles (I don't have specifics yet). They trade these for materials that come from the mainland, mainly crops and fabrics and more common metals.
If they have 'back flippers' then its just the feet; their legs are structured like humans. Whether or not they have flippers for feet/hands is just another genetic trait, like height.
The underside of a turtle shell is still quite hard, actually. Thus their chest is much better protected than a human's. Both the carapace (on their back) and the plastron ("underbelly") are for protection.

Kinda makes me think of Japanese Kappa. Not the same just makes me think of them. good job.