Shrimp like critter in live rock

[brandiswann]

Dipped some rocks today and a ton of these guys came out of the rock. Look like little shrimp. The picture is of one on the lip of a 5 gallon bucket. Pinky picture reference for size. Anyone know what these are and if they are good or bad?

 

[EeyoreIsMySpiritAnimal]

@ISpeakForTheSeas
@WheatToast

 

[PeterErc]

Mysid shrimp

 

[ISpeakForTheSeas]

The pic is (understandably) a bit blurry, but I’m relatively confident these are Anthuroidean isopods of some variety. Some genera that have similar looking species include Cyathura, Paranthura, and Tinggianthura.

not a lot of research has been done on Anthuroidean isopod diets, but the few studies that have been done found they preyed on amphipods.

So, unless you have some really tiny crustaceans that you care about in your tank, they should be harmless too.

 

[vetteguy53081]

Dipped some rocks today and a ton of these guys came out of the rock. Look like little shrimp. The picture is of one on the lip of a 5 gallon bucket. Pinky picture reference for size. Anyone know what these are and if they are good or bad?

This is a Tanaid which has more of an insectthan shrimp and is a member of the Peracarida group which includes both Mysids and Gammarid shrimps

 

[EeyoreIsMySpiritAnimal]

I have something similar in my tank... There are a ton of them in the sand bed and they curl up into a ball when disturbed.

 

[ISpeakForTheSeas]

This is a Tanaid

Tanaid is a solid guess too (and would be my second guess) - they can also look very similar to this, though I’m leaning a bit away from them in this case because species of Tanaids that have both similar head shapes and relatively small claws like this are much harder to find. Plus, Tanaids typically live in sand/mud, rather than rocks, so habitat-wise with these coming out if the rocks, isopods would seem to make more sense to me.

To complete my quote above for anyone curious about Tanaids:

Both should be harmless/beneficial - Tanaids are generally scavengers, eating detritus/herbivores, though a few eat worms and copepods; not a lot of research has been done on Anthuroidean isopod diets, but the few studies that have been done found they preyed on amphipods.

So, unless you have some really tiny crustaceans that you care about in your tank, they should be harmless too.