The Sealyham Terrier (Welsh: Daeargi Sealyham) is a rare Welsh breed of small to medium-sized terrier that originated in Wales as a working dog.It is principally a white-bodied, rough-coated breed, developed in the mid-to-late-19th century by Captain John Edwardes at Sealyham House, Pembrokeshire& Answered By: Ruthe Willms. Date created: Sun, Jun 27, 2021 4:21 PM. Sealyham Terrier - A Welsh breed, the Sealyham was named after the family estate of its creator, Captain John Edwardes, whose ...