Baby Trochus snails in skimmer

[Frogger]

Over the past 2 years I have pulled at least a dozen baby trochus snails out of my skimmer tube.

Now the amazing part of this is I have no trochus snails in my sump. They have to some how get from my tank, past my skimmer sock past the tunze skimmer pump and grow in the skimmer.

In my tank I have 5 types of snails, I have trochus, turbo, astrea, strombus sp. and nassarius. My strombus breed like crazy, I have hundreds, I have found them in my filter sock but never in my sump.

My only guess is the trochus gametes get past my filter sock either the gametes or the free swimming larvae really like the conditions in the skimmer and develop and grow in there. Anyone else experience this?