Stingrays are an enemy in most games, but most are passive and only deal damage if contact is made.
Ecco the Dolphin
In Ecco the Dolphin Common Stingrays are the default stingray. In the Master System version they appear earlier on in the game in Bay of Medusa, but in the normal games they don't appear until Ridge Water. They take two hits to defeat.
Defender of the Future
Stingrays are small white creatures that live in sandy areas on the ocean floor in Ecco: Defender of the Future. They are very hard to spot and if Ecco is swimming on the bottom they will attack him. They can be flushed out with the Sonar.