Worm comet

Sometimes there are streaks across the sky of great Sky Worms traveling in space. To the Tanuli and Dollies, worm comets are rare to see as they're usually not very visible from the water, although their presence is still felt in the rumbling of the ocean floor.
In Seed City, there are special sponge mansions that hold viewing parties for especially beautiful worm comets. While they don't necessarily serve a special magical purpose, they're beautiful.

Manifestation

Worm comets are slow-moving and thick streaks across the dark black sky. The streaks can be any length, from barely more than a circle to stretching across the entire sky like a band. Worms can be any color, but most Sky worms are brightly colored. The most anticipated comets are purple or blue in drastic opposition to the bright orange Moon.

Localization

In the sky above the Worm Sea is the Moon Worm, a Worm approaching from a distant area of space headed directly toward the Circles and their world. The creatures do not know that the Moon getting bigger is a sign of oncoming death of the world as they know it, but their creators do.
If a Worm comet is visible, the world is more prone to shivers as Little Circle and Circle shudder in their sleep in anticipation of the inevitable Moon Worm crash.