The Alfa 177 canine is a species of dog native to the planet Alfa 177. It is 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 Enterprise. After the transporter became infected with a yellow magnetic dust from the planet, they unknowingly tried to beam the canine back down. It rematerialized as two different dogs, one, a very gentle and shy one; the other was a very angry and dangerous one that would try to bite anyone who came near it, so it had to be put in a box in the transporter room. After they believed they repaired the transporter, they tried reintegrating the two. The results were futile, as the dog beamed back dead. (TOS: "The Enemy Within")