I don't know whether any of you have looked at the website I posted here yesterday, which has an old woodcut drawing of a Meerhase (as opposed to the photo of the sea-slug !). I reckon this is what the Brothers Grimm are talking about: a Mer-hare (like a mer-maid) half hare, half fish. Here's the website with the drawing:
I wouldn't mind having him nestling anywhere about my person !!