Updated photos of strange white growth

[Clementine]

I posted a few weeks ago (though now I can't find any previous posts that I've made!) about a strange white line that started across Igloo's back. The line has grown bigger. Still no idea what or why it's there...any ideas?Previous growth.
Today's growth

 

[AmRoKo]

Whoa, too me it looks like marbling but I'm not sure, someone else with more experience will have to come here and help you out.