Debbie was a bloop that Penny Robinson acquired as a pet during her time on Preplanis. ("Island in the Sky")
On one occasion, Debbie temporarily grew to enormous proportions after eating some exotic fruit. ("The Oasis")
Debbie was played by Tonga the chimpanzee. The giant version of Debbie was portrayed by Janos Prohaska.
In the original, unaired pilot, there was a bloop named Debbie as well. ("No Place to Hide") Due to the plot changes between this episode and "Island in the Sky", one can assume these were two different bloops.
Debbie was featured in Lost in Space Annual #2, "Whatever Happened to Baby Bloop?".