Is this the first time the Sea Siren was used? Has it been used since? (Inquiring minds want to know.)

I have a suggestion for the difference between Golden & Silver Aged- Aquamen. Could Topo be Silver and the unnamed Sea Cow be Golden allies?

Yes to the first question, I'll find out as I keep reading to the second one...

As for Topo and the Sea Cow, yup! I think that's pretty much it.