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It seems so unlikely eggs would avoid predation and mechanical filtration especially if laid on the glass.May be that way
Sincerely Lasse
I don't think they lay eggs on glass in the wild.It seems so unlikely eggs would avoid predation and mechanical filtration especially if laid on the glass.
Maybe they were laid in a rock crevice in your tank.
1/3 of size of the others. A size you not have introduce. What do you think happens? Parthenogenesis (virgin birth)? or "bean me down, Scotty"It seems so unlikely eggs would avoid predation and mechanical filtration especially if laid on the glass.

far more likely to have come in as hitchhikers.1/3 of size of the others. A size you not have introduce. What do you think happens? Parthenogenesis (virgin birth)? or "bean me down, Scotty"
Sincerely Lasse
We do not know how old the tank is and if use dry or live rocks. Hitchhiker is one possibility - but we do not know. I have had reproduction of turbo snails in my aquarium.far more likely to have come in as hitchhikers.
That's curious because 1-2 months as plankton seems too long to survive filtration in a reef tank.I just did a fast search. This may be of interest:
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Nassarius Snail – Detailed Guide: Care, Diet, and Breeding - Shrimp and Snail Breeder
Nassarius snails are super easy to keep and feed. In addition, they are very resilient and can tolerate a wide range of water parameters.aquariumbreeder.com
"The life cycle of the Nassarius snails is characterized by the presence of planktonic veligers (larvae) that emerge from benthic capsules.
The planktonic larvae require 1–2 months to complete metamorphosis and settlement. That is a relatively long planktonic phase compared to other gastropods.
The Nassarius snails usually attach their egg capsules to hard substrates (the glass of an aquarium, rocks, decorations, etc). Each egg capsule can contain from thirty to – several hundred embryos, which developed until the veliger stage is reached.
Hatching takes place after about 9 – 15 days of encapsulated development. The complete larval development and metamorphosis throughout 25 – 35 days."
Seems unlikely, but if we are speaking of just a few survivors as we seem to be here, it is conceivable. Even with good flow and high tank water turnover by filtration, I don't see how every molecule of water nor every planktonic critter riding within the water passes through the filter, even over a long time. I could be wrong, but as an example, eddy currents caused by pockets in rocks could themselves account for a bit of water that churns for a long time without getting filtered.That's curious because 1-2 months as plankton seems too long to survive filtration in a reef tank.
Yes, the snails with direct development would be the only way to reproduce in a reef tank in my opinion.Here is a Nassarius species with direct development. Not all have a planktonic larval stage.
Sincerely Lasse