Larva, one a lizard periodically rejected (5)
I believe the answer is:
naiad
'larva' is the definition.
(I have seen 'Aquatic larva' mean 'naiad' so perhaps 'larva' could also mean 'naiad')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for naiad that I've seen before include "spirit in water" , "Aquatic larva of a dragonfly" , "Diana (anag.)" , "Classic spirit" , "Fabulous spring being" .)