The most common and most likely answer to this crossword clue is the 6 letter word HIPPOS
I've seen this crossword clue in Financial Times
H
I
P
P
O
S
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The straight part
We know that "animals" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case animals = hippos.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HIPPOS mean?
HIPPOS noun- A large, semi-aquatic, herbivorous (plant-eating) African mammal (Hippopotamus amphibius)