Bug (a verb) - enter it wrongly (12)
'bug' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'a verb enter it wrongly' is the wordplay.
'wrongly' indicates anagramming the letters.
'averbenterit' with letters rearranged gives 'INVERTEBRATE'.
Can you help me to learn more?
(Other definitions for invertebrate that I've seen before include "Sort of creature", "missing cord", "Animal without a backbone", "leech, say", "Backboneless creature".)