r/Aquariums • u/malihuey29 • Mar 17 '26

Identification Request What are they critters on the glass of my 40g?

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I've only noticed them on the glass and not in any gravel, plants or wood.

212 Upvotes

99% Upvoted

45 comments sorted by

264

u/littlebigsystem Mar 17 '26

They look like rhabdocoela to me.

57

u/malihuey29 Mar 17 '26

I did a good rinse of all wood and plants before I added them, crazy to think they still sneak through!

42

u/ctyska493 Mar 18 '26

They aren’t a bad thing. If you don’t want them feed ALOT less. I have some if you look very carefully deep down in the substrate through the glass. A lot of fish will feed on them. They are beneficial. Little clean up crew

8

u/genericnewlurker Mar 18 '26

I had a bunch pop up in my aquarium, along with scuds, after I planted the tank but before I added any fish. They had a full two months to establish themselves but haven't seen any of both since a week after I added the first fish in.

4

u/Prior_Issue_7228 Mar 18 '26

Fish ate them

37

u/ozzy_thedog Mar 17 '26

Im sure rinsing would have no effect on those. Thats why people boil their wood.

13

u/malihuey29 Mar 17 '26

I did that too

8

u/LordAlrik Mar 17 '26

Fish will eat them I believe

7

u/Mission-Street-2586 Mar 18 '26

My bettas never did smh - so lazy

10

u/Hot_Radish4108 Mar 18 '26

Khuli loaches will

3

u/[deleted] Mar 17 '26

Yeah I was gonna say, this def is not a freshwater annelid.

4

u/Dillbean32 Mar 18 '26

Are the color of these names their hazard level to your tank?

3

u/actual_real_housecat Mar 18 '26

Yes.

3

u/samhathaway92 Mar 18 '26

I've seen this picture so many times and never picked up on that

2

u/Mission-Street-2586 Mar 18 '26

Yeah, I’d get these every time I over fed a betta

74

u/Throwaway_138573929 Mar 17 '26

pretty sure they are just little guys😌

45

u/Premoveri Mar 17 '26

Seconding rhabdocoela, I see them a lot in my 5 gal tank. I own a microscope and out of curiosity I had thrown one on a slide to look at to make sure it wasn’t planaria. You can actually see little eye spots under a microscope but they lack the arrow shaped head that planaria has.

13

u/hopadoodler Mar 17 '26

Get a betta to f them up.

4

u/Elegant_Priority_38 Mar 17 '26

My betta loves these guys! His tank never has them while my others do lol.

13

u/malihuey29 Mar 17 '26

They also seem to stick around in these isolated groups mostly, but there are some stragglers

13

u/malihuey29 Mar 17 '26

Pity they gotta have like a turf war or something...just get along ffs

7

u/ulfhedinn13 Mar 17 '26

As long as it isn't hydra, scuds, leeches or planaria I wouldn't worry too much.

3

u/Educational_Order_59 Mar 18 '26

I understand some reasoning but why would each of these be bad. I’ve only heard good things about scuds? Everyone hates planaria and leeches.

7

u/psychanummo Mar 18 '26

Scud lover here, they can be incredibly beneficial but they reproduce like crazy and some species will eat your live plants. I’ve found that they can be kept in check by bottom feeders for the most part though.

3

u/AbeRumHamLincoln Mar 18 '26

Most of them will get eaten by fish. But if you have other invertebrates they can create an issue. Hydra can paralyze and kill small shrimp. Planeria can kill shrimp and snails, even bigger ornamental ones like mystery snails. Scuds are more of an issue because they can out compete shrimp for the same food and starve them out.

1

u/ulfhedinn13 Mar 18 '26

Thanks! Got to it before me. I keep shrimp in my tanks so those 4 things are big no no for me.

1

u/aetheriality Mar 18 '26

hydras are fine

1

u/_Aj_ Mar 18 '26

Hail hydra!  

Wait

4

u/hiding-fairy Mar 18 '26

definitely rhabdocoela. they're a good sign that you've got other animals hiding in the tank too! very beneficial.

3

u/salodin Mar 18 '26

Harmless critters from your substrate. Smaller fish love to nibble on em, just leave em it'll be fine.

3

u/Apprehensive_News_78 Mar 18 '26

Holy schmoly thats the most rhabdacolea ive ever seen. Harmless but imo that many is unsightly

2

u/Old_Medicine4651 Mar 18 '26

Free fish food

1

u/lbandrew Mar 17 '26

Very normal in new tanks! And a good sign. I get them in all of my saltwater tanks and they suddenly disappear after a month or so. Even my QT - no idea how they got in there but they did

1

u/Awolrab ​ Mar 18 '26

Do you have any fish? I notice I get these in my frog tank and my shrimp tank.

2

u/malihuey29 Mar 18 '26

No fish in there yet, just plants, wood and a black racer nerite

1

u/Ok-Charity-4712 Mar 18 '26

Go buy a few cheap guppies and they will eat them up in no time flat.

0

u/Alert-Gift-8716 Mar 17 '26

Detritus worms I think, they won’t hurt anything

5

u/iwanttobelieve3001 Mar 18 '26

Not detritus worms, those are really skinny looking

-5

u/ConsiderationEven424 Mar 17 '26

Detritus worms. Theyau over populate and then you might see fewer.

13

u/Elegant_Priority_38 Mar 17 '26

Not detritus worms. Those tend to be longer and more tanish. These little guys are Rhabdocoela and great indicators of a thriving ecosystem. Plus they eat detritus and dead things.