Hair that's long and poorly groomed (6)
I believe the answer is:
shaggy
(Other definitions for shaggy that I've seen before include "Describes thick and poorly groomed hair" , "like the dog in the story" , "Unshorn - Scooby Doo's pal" , "Hairy and unkempt" , "Funny as a story about a type of canine" .)