A daggit is a canine-like animal used as a domesticated pet, watch animal, or tracker. No daggits survive the Cylon holocaust.
Boxey loses his daggit, Muffit, to the destruction on Caprica.
A robotic counterpart similar in appearance to a daggit, named Muffit II is built by Dr. Wilker and presented to Boxey (TOS: "Saga of a Star World").
Like a real daggit, the new Muffit proves its bravery and dedication to protecting humans during a dangerous fire aboard Galactica (TOS: "Fire in Space").
Additional mechanical daggits are briefly seen in the pilot episode of Galactica 1980.
In the re-imagined series, dogs are simply called dogs, and unlike the original series, a number of these pets (e.g. Jake) survive the holocaust within the Fleet.
Original Series definition: a domesticated canine, e.g. dog (see: daggit)