Pygmies are a specific morphology known for their small size, and are only able to breed with other Pygmies, including Pumpkin Dragons. Most of these dragons on Dragon Cave will have "Pygmy" in their name somewhere. Pygmy eggs cannot be bitten by Vampire Dragons due to their size.
On August 20, 2017, a site update wherein new descriptive text for this morphology type was added to a pygmy dragon's page. This text is included in addition to the regular dragon description, going underneath it, and it describes what pygmy dragons are in the context of the Dragon Cave world.