According to Wikipedia the Crab-eating frog is the only amphibian that can survive in sea water. However Wikipedia also suggests that it can only survive
brief excursions into the sea.
There are no such things as sea frogs.
Even the Crab-eating frog doesn't live in the sea though. Its natural habitat is mangrove swamps.
The crab-eating frog (Fejervarya cancrivora), is a frog native to south-eastern Asia including Taiwan, China, the Philippines and more rarely as far west as Orissa in India. It inhabits mangrove swamps and marshes and is the only known modern amphibian which can tolerate brief excursions into sea water.
This frog can tolerate marine environments (immersion in sea water for brief periods or brackish water for extended periods) by increasing urea production and retention, and by remaining slightly hyperosmotic within urea and sodium flux. Adults can survive in salt water with salinity as high as 2.8%, and tadpoles can survive salinities as high as 3.9%.