In the manga, Seiya was actually trying to fled from the Colosseum, but Marin found him in the end. In the anime, that scene was left out.
Of the several differences between the manga and the anime, the most visible one is the Bronze Armors' design in the Sanctuary Arc. As the Saint Seiya anime was first aired on TV, the Cloth worn by the main characters came as a surprise to the manga readers.
In the manga of the Sain Seiya series, you could see the face of Marin, but in the anime they left that out.