What does the cryptic crossword clue "Tree-dwelling mammal the rest held too in a nervous fashion (5,4,5)" mean?

The wordplay uses an anagram. anagram of THE + REST + HELD + TOO = THREETOEDSLOTH The answer is THREETOEDSLOTH.

Tree-dwelling mammal the rest held too in a nervous fashion (5,4,5)

Daily Mail Cryptic #17277 | 6 Across | 2024-01-23 flower