Jellyfish larvae, hydroid medusa

In My Humble Opinion
1

They resemble a tiny badmitton birdies, and show up occasionally as pests in marine aquariums.
I’ve been attempting to raise neon goby fry, larval like beings themselves, requiring very small food and have had an increase in these creatures.
My best guess is that they come from the foods I need to raise fry:
Brine shrimp egg hatching
Marine rotifers
Home grown micro algae I have purchased.

Does anyone have experience with these creatures, or a knowledge of marine biology to tell me how they got into my aquarium?
Thanks.

2

I think those are just young jellyfish, they start from anchored polyps, not really larvae, and you have listed some of the ways they could have entered your tank. They could have been in any water your fish came with also.