Pekingese

A Penkinese is a magical creature mentioned in the Half Blood Prince, where Rubeus Hagrid compares the size of Aragog at birth to one. Nothing about the creature is known, however, it is suspected that they are relatively small.

"I had him from an egg, yeh know. Tinly little thing he was when he hatched. Bout the size of a Pekinese" - Rubeus Hagrid at Aragog's funeral