We may take the seal to be another animal altogether (6)
I believe the answer is:
weasel
'another animal altogether' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'we may take the seal to be' is the wordplay.
'may take' means one lot of letters go next to another.
'to be' is an anagram indicator.
'seal' with letters rearranged gives 'asel'.
'we'+'asel'='WEASEL'
Can you help me to learn more?
(Other definitions for weasel that I've seen before include "Small fierce animal with slender body and reddish fur" , "Double-dealer" , "Small fierce animal with slender body and reddish-brown fur" , "Predator" , "These animal words are intentionally misleading" .)