Snapper arrived before tailless ray (6)
I believe the answer is:
camera
'snapper' is the definition.
(cameras go snap)
'arrived before tailless ray' is the wordplay.
'arrived' becomes 'came' (come can mean to appear or arrive).
'before' means one lot of letters go next to another.
'tailless' means to remove the last letter (the tail of the word is removed).
'ray' with its last letter removed is 'ra'.
'came'+'ra'='CAMERA'
(Other definitions for camera that I've seen before include "TV/film equipment" , "source of shots?" , "brownie perhaps" , "in judge's private room" , "Image recording apparatus" .)