The flounder is an ocean-dwelling flatfish

Flatfish

The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...

 species that is found in coastal lagoons and estuaries

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 of the Northern Atlantic and Pacific

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 Oceans.
There are a number of geographical and taxonomical species to which flounder belong.

• Western Atlantic
  • Gulf Flounder - Paralichthys albigutta
  • Southern flounder
    Paralichthys lethostigma
    Paralichthys lethostigma is a popular sports fish and is the largest and most commercially valuable flounder in the western north Atlantic ocean and Gulf of Mexico. Its range is North Carolina to the Yucatan peninsula...
    
     - Paralichthys lethostigma
  • Summer flounder
    Summer flounder
    The Summer Flounder is a marine flatfish that is found in the Atlantic Ocean off the East coast of the United States and Canada. It is especially abundant in waters from North Carolina to Massachusetts.-Description:...
    
     (also known as fluke) - Paralichthys dentatus
  • Winter flounder
    Winter flounder
    The winter flounder, Pseudopleuronectes americanus, is a right-eyed flatfish of the family Pleuronectidae. It is native to coastal waters of the western north Atlantic coast, from Labrador, Canada to Georgia, United States...
    
     - Pseudopleuronectes americanus

• European waters
  • European flounder
    European flounder
    The European flounder is a flatfish of European coastal waters from the White Sea in North to the Mediterranean and the Black Sea in South. Introduced into the USA and Canada accidentally through transport in ballast water. It is a well-known food fish.-Description:The European flounder is oval in...
    
     - Platichthys flesus

• Off the coast of Japan
  • Olive flounder
    Olive flounder
    The Olive flounder or Bastard halibut is a species of large-tooth flounder native to the north-western Pacific Ocean....
    
     - Paralichthys olivaceus

In its life cycle, an adult flounder has two eyes situated on one side of its head, where at hatching one eye is located on each side of its brain.