Is there a sea form island in Pokemon crystal?

While there is no island shaped like a seahorse in Pokemon Crystal, there is a seahorse Pokemon called Seadra**. This Pokemon is a rare evolution of a Horsea and can be found in the waters surrounding the islands in the game.

There are also several islands that are shaped like other sea creatures, including:

* The island where the legendary Pokemon Lugia is found resembles a whale.

* The island where the Pokemon Center is located near Ecruteak City resembles a dolphin.

So while there isn't a seahorse island, Pokemon Crystal does have plenty of sea creature-inspired geography and Pokemon!