A Umi-No is also known as a Tamagotchi ocean (or Oceangotchi). It is a little harder to find than an Angelgotchi, and a little more expensive also. It as ocean themed things, such as characters, games and even a 'preview' screen before you start.
This Tamagotchi is the hardest Tamagotchi released ever. I personally have never made it to an adult before. It dies easily and can even get hurt by a polar bear.