Crossword Genius

It has a gentle wriggle (6)

Ross

I believe the answer is:

maggot

I'm a little stuck... Click here to teach me more about this clue!

'gentle wriggle' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'it has a' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
'a' is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for maggot that I've seen before include "Lava of a fly" , "youngster to fly" , "pest" , "Legless grub" , "immature flyer" .)

I've seen this clue in the Evening Standard.
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