Answer:
Flat as a leaf, round as a ring; have two eyes, can't see a thing. What am I?
I am the key that is the hardest to turn
When I come in from sea to shore twenty paces you'll see No less no more.
I am a busy worker who is a water mammal.
I am merry creature in pleasant time of year as in but certain seasons I sing that you can hear; And yet I'm made a by-word A very perfect mock; Compared to foolish persons And silliest of all folk.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.