Tiny little creatures in 20 gallon tank

[Travis93]

I have a 20 gallon that's got some shrimp, rasboras, a dwarf gourami, and some African dwarf frogs in it. I noticed today that I have these tiny little things in the tank. It looks like they are eating off the gravel. I'm not sure if it's baby shrimp or tadpoles or what. I've attached a picture.

 

[Fresh2o]

Seed Shrimp (Ostracods)

 

[Travis93]

Seed Shrimp (Ostracods)

Are they something I should be worried about? And how would I have gotten them?

 

[Fresh2o]

Nothing to worry about. Probably arrived with new plants or driftwood (it was submerged).