Finally caught one. Anybody know

[Levinson]

There are a lot of these tiny amphipod/isopod/shrimp like fellas in my tank. They like to hide in the holes on the rocks or under the sand.
I've been meaning to get a closer look at these guys and I managed to catch one while cleaning.
Does anyone know what they are?

 

[Zach B]

Tropical mysid? Looks different from an amphipod to me as well

 

[William Mumford]

Amphipod good guy. Wrasse love them. I have tons in my sump.

 

[Tired]

Amphipod. Normally harmless and good fish snacks, but particularly large ones or large amounts of them can be trouble. They'll eat stressed corals, and can turn an unhealthy coral that could recover into an empty plug. Fish usually keep them relatively under control.

 

[Soren]

That looks different than the typical gammarid amphipod, but it does also have some similarities.

 

[Clownfish_Boy]

Great Mandarin food ! Would love to have some in my tank !

 

[Levinson]

Thanks, all.
I have only sexy shrimps, couple of bristle worms, collonista snails and pods. No coral nor fish. Nothing that would actively hunt and eat these guys but or that they would attack. No problem then I guess?

 

[LRT]

Thanks, all.
I have only sexy shrimps, couple of bristle worms, collonista snails and pods. No coral nor fish. Nothing that would actively hunt and eat these guys but or that they would attack. No problem then I guess?

Doesn't sound like you have much to worry about considering you have no corals and shouldn't be harmful to your other critters.
That being said and answer to your question. YES they can become a problem if left unchecked. Populations can explode without natural predators. And contrary to popular belief there are plenty of amphipods that are carnivorous. They will eat healthy corals as well as stressed corals and even mysis shrimp and krill. Especially when no other food source is available. I watch them snatch and eat pieces of mysis and krill daily when I feed my fish in my sump.
Plenty of horror stories of Amphipods eating corals available with quick Google search.
I say your fine. Until you add coral.