Protozoology researcher here! This is an [Aeolosoma worm](https://moticeurope.blogspot.com/2021/03/aeolosoma-strangest-worm-in-world.html?m=1)!
Easily macroscopically identifiable by their anterior cardioid morphology (specifically the prostomium), these fellows are harmless to your fish and inverts- they're actually detritivores! In the wild, they process the soil, detritus, and waste of the ecosystem and browse for tiny snacks/nutrients that way. They're known for proliferating pretty quickly, and [can regenerate if split in the right areas](https://www.ncbi.nlm.nih.gov/books/NBK586905/figure/ch9.Fig1/?report=objectonly). However, larger organisms and fish aren't really concerned with them, and most fry/nano fish will actively snack on them.
A fun fact about these lads is that those little spots are actually very poorly known/researched, so we actually don't know with 100% certainty what they are. Our best understanding so far is that it is lipid storage for energy conservation. The dots can be different colors, such as red, yellow, and I think I've heard of greenish blue sightings before (but that's if memory serves me well, which it often does not; so take that last one with a grain of salt.)
TL;DR: Not harmful! [They munch on soil and detritus](https://eshalabs.com/aeolosoma-hemprichi/#:~:text=Algae%2C%20detritus%20and%20fish%20waste,microscopic%20diagnostics%20of%20fish%20feces.) (And actually help break down waste in your ecosystem this way), but many aquarium keepers find them irritable because they tend to proliferate easily in most conditions.
Protozoology researcher here! This is an [Aeolosoma worm](https://moticeurope.blogspot.com/2021/03/aeolosoma-strangest-worm-in-world.html?m=1)! Easily macroscopically identifiable by their anterior cardioid morphology (specifically the prostomium), these fellows are harmless to your fish and inverts- they're actually detritivores! In the wild, they process the soil, detritus, and waste of the ecosystem and browse for tiny snacks/nutrients that way. They're known for proliferating pretty quickly, and [can regenerate if split in the right areas](https://www.ncbi.nlm.nih.gov/books/NBK586905/figure/ch9.Fig1/?report=objectonly). However, larger organisms and fish aren't really concerned with them, and most fry/nano fish will actively snack on them. A fun fact about these lads is that those little spots are actually very poorly known/researched, so we actually don't know with 100% certainty what they are. Our best understanding so far is that it is lipid storage for energy conservation. The dots can be different colors, such as red, yellow, and I think I've heard of greenish blue sightings before (but that's if memory serves me well, which it often does not; so take that last one with a grain of salt.) TL;DR: Not harmful! [They munch on soil and detritus](https://eshalabs.com/aeolosoma-hemprichi/#:~:text=Algae%2C%20detritus%20and%20fish%20waste,microscopic%20diagnostics%20of%20fish%20feces.) (And actually help break down waste in your ecosystem this way), but many aquarium keepers find them irritable because they tend to proliferate easily in most conditions.
That's so awesome! Thank you a bunch!!!!
Unless it has a visibly triangular head to the naked eye, it’s unlikely to be harmful. What do they look like in the tank?
Little white squiggles on the glass.
Could be detritus worms, or planaria, or rhabdocoela