Race and Dr. Quest are playing a chess game before the boat catches fire. When the camera cuts back once, there are no pieces on the chess board.
Judging by their size and strength, it's reasonable to assume that these animals were one of the gorilla species. Male gorillas weigh anywhere from 350 to 600 pounds. Both "Silky" and "Chopper" were jumped on by these creatures several times. A creature that heavy jumping on a man would likely kill him; about the best he could hope for would be serious injuries. Yet at the end of the episode, "Silky" and "Chopper" are apparently unharmed. "No actors were harmed during the production of this cartoon!"
The location and the appearance of anthropoid apes is almost the same found in Edgar Rice Burroughs' "Tarzan of the Apes".