This page lists worlds which received relatively little mention in the book.
Dragon Planet is the native world of the Dragons. Its atmosphere is very thick more like water than air.
The Spiders' World
The Spiders' home world is cold and gray.
The See Weeds' World
The See Weeds' world has a vast ocean.
The Dolphins' World
The Dolphins' world also has an inhabited hydrosphere.
Whether Summer World is a world in its own right or a synonym for a world such as Planet of the Flowers is not utterly clear (though the fact that Summer World was one of the first planets the Souls colonized while Planet of the Flowers is the furthest planet from Earth that is still open for new Souls seems to suggest so).
There also seem to be other unnamed worlds the Souls colonized but are not open for new Souls.
There are also many uninhabited celestial objects.