Jacondans were humanoids with large, pointed noses, grey skin, feathers instead of hair and small horns growing from their brows. These feathers came in a wide variety of styles and lengths and grew in the same places as eyebrows, moustaches and beards.
Jacondan mythology claimed that one of the queens offended the Sun God, which made him release the original Gastropod. This giant Gastropod produced many offspring, who devoured all food on the planet. The Sun God saw what he had done and relented, causing a drought that killed all of the Gastropods.
This mythology was at least partly true and at least one of the Gastropods lived. These Gastropods conquered Jaconda while Azmael was in power. The giant Gastropods took over Jaconda using their telepathic abilities and devoured all available vegetations on the planet. Food was scarce for the Jacondans, so they resorted to theft and disobeyed their masters.
To end the famine, Mestor, the Gastropods' leader, commanded Azmael to bring the two nearest planets into Jaconda's orbit. Azmael believed they would be used for growing food and kidnapped two geniuses from Earth, Romulus and Remus Sylvest. The Sixth Doctor, Peri and Lieutenant Hugo Lang discovered this kidnapping and followed Azmael to Jaconda. There, the Doctor figured out that Mestor's plan was to destroy Jaconda by sending the two planets into the sun, allowing the Gastropods' offspring to be released across the universe. Azmael was able to stop Mestor, though he was killed in the process. At this time, the Jacondans were released from their telepathic mind control. (TV: The Twin Dilemma)