Is worms a pest or friend for planted tank?

[naturetan]

Recently discovered something strange crawling creatures underneath my substrate sand. It looks like a caterpillar/worm which is very light greenish white in color about 2mm diameter & 10mm length. It's residing at the outlet of the water inside the sand, and there're two of them.[:0] Not sure what are they and where they come from.

Are they a friend or a pest? In nature, I understand that worms play an important role in conditioning well the soil, thus helping the plants grow better. How about underwater? What are the roles they play? Could they have laid lots of eggs (like snail) and multiply to hundreds in population?

Hope someone well-read can enlighten me before deciding whether to remove it or not.

[bclee]

Worms = fish food []

But seriously... never heard of this type of worm.

Interesting...

BC

[kc]

If it got 4 or 5 tentacles, it is hydra. It can attack fries.