Not flatworms, so what are these dots really?

[ficertyn]

I asked a few days ago what the little dots that hitched a ride with my cerith snails could be.

It seemed like several thought flatworms. I brought them to my LFS so that they could take a look and be aware that these were in with their snails. They took a look and while we were unable to identify what they are, the consensus was that they were not flatworms.

Size: < 1mm
Free Swimming
Red
Attracted to light

We put them under a microscope, and they look like they have an almost clear tail, and are the shape of a tadpole.

Any ideas?

 

[Tahoe61]

Type of Flatworm. There are literally thousands of types. Almost never rely on the LFS to give you the correct ID on a product they sold you.
Those look like they might be benign.

 

[Uncle99]

Flatworms. They can multiply fast.

Salifert makes a product called flatworm exit.
Some wrasses pick at them.

 

[StradicCi4]

Still flatworms lol

 

[ISpeakForTheSeas]

I asked a few days ago what the little dots that hitched a ride with my cerith snails could be.

It seemed like several thought flatworms. I brought them to my LFS so that they could take a look and be aware that these were in with their snails. They took a look and while we were unable to identify what they are, the consensus was that they were not flatworms.

Size: < 1mm
Free Swimming
Red
Attracted to light

We put them under a microscope, and they look like they have an almost clear tail, and are the shape of a tadpole.

Any ideas?

Fluke cercariae (you can just barely see the tails you mentioned in that last pic) - I'm not well-versed in flukes yet, so I believe these may need a new host (they were likely previously hosted by the snails) to complete their transformation to adult flukes which may infect fish; @Jay Hemdal probably knows better though.

 

[Jay Hemdal]

Fluke cercariae (you can just barely see the tails you mentioned in that last pic) - I'm not well-versed in flukes yet, so I believe these may need a new host (they were likely previously hosted by the snails) to complete their transformation to adult flukes which may infect fish; @Jay Hemdal probably knows better though.

Yes digenean trematodes require multiple hosts, most commonly snails as one of them. They can also infest fish and birds in complicated life cycles. The metacercarie (spelling?) larva look like tadpoles.