Jessie's Arbok was most likely Jessie's first Pokémon. She got it as a Ekans for her birthday. Eventually it evolved into an Arbok because Jessie wished desperately for it to. It was later released to protect a group of Ekans from a Pokémon Poacher. When Jessie told it to stay behind and protect the Ekans, it started crying.
In The Misty Mermaid, Arbok was shown to be able to swim without needing to breathe.
In The Island of the Giant Pokémon, Arbok (as an Ekans) said that it's not bad, but do bad things because of Jessie being bad.
Note: Bite was classified as a Normal-type move at the time of its first usage.