Two entries with the name Jonas.
Jonas
A hermit priest encountered by Perceval in a forest. His companion was named Alecys.
Source
Perlesvaus | Early 13th century
Jonas
The first husband of Trephina, daughter of Warok, and father by her of Judwal or Tremeur.
It is possible that the couple remained childless, for Tremeur is also named as the son of Cunomorus, who was also, at some stage, married to Trephina.
See also
Venetii | The Legend of King Arthur