Opossum has 7 letters in it. But the "o" is not pronounced(I mean, uh, said?).
DORMICE
Groundhog.
Mouse.
coypu
paca
Rat
rat
The Pika
There is no planet whose name contains 9 letters
Lemming
Lemming
paca
Rodent
The paca is a large burrowing rodent of South and Central America.
Stephane