Hi SS well this is a possible spoiler, but you CAN cross a certain fin type to silky and get ... SILKY!!! There is only one cross that I know of, unless it is also with finless, which I haven't completed yet.

Check here for hint ( Here big kitty!! 'big kitty' + silky = silky)

But in all that I have done (and I didn't look at anyone's charts either -- I'm doing it from scratch and made my own LOL), I haven't come across any crosses for Spotanus yet, and I am about 90% done on body type. I have found or bred all but three of them. Thank goodness you can buy eggs at the store!!

And, YES save all Twin Fins ... at least you can breed a Twin Fin of one to another Twin Fin to get new species .