Krabby, or just Crab in Japanese, was a small water type Pokémon that resembled a real life crab.
In the anime Ash inadvertadly insults a small Krabby about its size, angrily the Krabby attacks, not bothering useing one of his pokemon he uses a stick to defeat him and then captureing it in a pokeball. Afterwards the Krabby goes into storeage at Proffesor Oak's Lab, causeing ash to panic about the wereabouts of his recently caught Krabby but misty informs him that he can only have six Pokemon at a time. Later Krabby is used to defeat an Exeggutor and evolves into Kingler after beating it, the Kingler is still used by Ash.