I've heard the same line sung about the oysters in "The Virgin Sturgeon"

The oyster is a bivalve molusc
You can't tell the he from she
...something, something, something, something...
but he can tell and so can she.

Wish I could remember the third line, but it was back in '58 when I heard that one, so you'll have to make one up for yourself.

Bert.