(urth) Inhumi in the Whorl

[Lee Berman]

>James Wynn: Well, the inhumi were such masters of disguise that almost nothing they 
>did would surprise me.
 
If we are wondering if the Whorl came with Inhumi, it seems we should be looking for
evidence of shapeshifting vampires on Urth.  Shapeshifters are mentioned in BotNS.
albeit in stories. What is the source material of those stories?
 
Dorcas thinks Severian looks like a  black bat who has been sucking blood all night
after he eats a pomegranate. We are told often of blood bats and we see the wounds
they supposedly make. But do we ever actually see one?
 
We are also told of manatees and we never see those either, though we do see the undine(s)
that manatees are fairly clearly a euphemism for. What might blood bats be a euphemism for?
 
Moreover, Urth used to be the hub of an empire of 10,000+ planets. It hardly seems impossible
that one of the millions of spaceships flying around managed to land on Green and its cargo
eventually made it to Urth. What are the sources of the legends...?