Zistles are composed of blue, irregular crystal lattices. Their body shows a vaguely spherical symmetry, without any limbs or orifices. However, they do appear to have root-like appendages in the lower part of their body.
Temperatures higher than -250 ºC (-418 ºF) are uncomfortably warm to them. They are likely capable of electroreception, as the book describes that nighttime allows them to communicate better due to higher electric conductivity.
Despite lacking significant motility, zistles are able to jump up to 20 meters under their home planet's low surface gravity.
Zistles make use of the increased electric conductivity at night to spend it "radioing great thoughts to each other." Unaware of life on Earth, zistles think of Pluto as the only life-harboring world.
- Galant, Roy A. "Picture Atlas of Our Universe". National Geographic. p 46.