Tiny mollusk critter id please

[xeniafarmer]

There are many (>100) of these crawling on the glass of my 2 month old mixed reef. The largest are about .8 mm (1/32 in.) long. Some have a dark U shaped line. They are too small to see from a side view to tell if they have a shell or other dorsal structure.

Thanks,
Dave

 

[greenbean36191]

[welcome]
They're harmless acoel flatworms.