The Alfa 177 canine was a species of dog native to the planet Alfa 177. It was very similar to an Earth dog, with the exception of a horn on its head, a scaled backbone, and thin gold antennae sprouting from its head.
In 2266, a specimen of this species was brought aboard the USS Enterprise. After the transporter became infected with a yellow magnetic dust from the planet, the crew unknowingly tried to beam the canine back down to the surface of Alfa 177. The animal rematerialized as two different dogs: one, very gentle and shy, and the other very angry and dangerous, who would try to bite anyone who came near it, so that it had to be put in a box in the transporter room. After the crew came to believe that they had repaired the transporter, they tried reintegrating the two. Although the procedure itself appeared to be a success, the animal was found dead, possibly due to the shock of reintegration. (TOS: "The Enemy Within")