"Sunny side up egg" algae(?) on glass

[formallydehyde]

I thought these were some kind of flat worm at first but when I scrape them off the glass they seem calcified so I assume they're a type of algae. They're probably a bit less than a centimeter, the side facing the glass looks like a fried egg with a bright yellow-with-hint-of-green "yolk." The side not facing the glass is just white and slightly rounded.

They're mildly annoying but don't seem harmful, I'm just curious what they are.

 

[zoomonster]

I would say snail eggs of some sort

 

[ISpeakForTheSeas]

If you've got any Nerite snails, those would be my guess.

 

[FurrierTransform]

If they move around, then I would say they are limpets.

 

[formallydehyde]

If you've got any Nerite snails, those would be my guess.

I have a single Nerite snail

 

[ISpeakForTheSeas]

I have a single Nerite snail

That's unlikely then. Do they move around? If so, then I'd agree with FurrierTransform that they're likely limpets.

 

[formallydehyde]

That's unlikely then. Do they move around? If so, then I'd agree with FurrierTransform that they're likely limpets.

As far as I can tell they don't move around, and I don't see any mouth parts on them.

 

[ISpeakForTheSeas]

As far as I can tell they don't move around, and I don't see any mouth parts on them.

What other snails/sea slugs do you have in your tank (if any)?

 

[formallydehyde]

What other snails/sea slugs do you have in your tank (if any)?

I have:
Two strawberry conches (they climb on the glass but not typically the front)

Two lettuce sea slugs of different species (Elysia clarki and Elysia diomedea) - guessing it's not them because of the characteristic spiral pattern their eggs are laid in and the fact that they're different species.

Three or four small nassarius snails.

I used to have a bunch of collonista snails but I think they stopped breeding and died off because I haven't seen any in a while. I have a few more snails too but they were added after these things started appearing.

Any chance nerite snails can lay unfertilized eggs?

 

[ISpeakForTheSeas]

Interesting. I doubt the nerite will lay unfertilized eggs (and the yellow center would seem to indicate that they are fertilized), so I doubt that one’s the cause here. I’ve heard that some Nassarius snail species will lay singular egg sacs instead of the usual, massive pattern of eggs, but I can’t confirm this at the moment, and that would be pretty unlikely too from what I’ve seen.