"We show that 558-million-year (Ma)-old tube worm-like #Calyptrina and mollusc-like #Kimberella possessed a gut and shared a #diet of green #algae and bacteria. Despite their ancient age, sterol #metabolism within the gut of both organisms was already comparable to extant invertebrates. 
#Dickinsonia, one of the key #Ediacaran animals, show no traces of dietary molecules, indicating a different feeding mode and possible external #digestion analogous to modern #Placozoa."

https://www.cell.com/current-biology/fulltext/S0960-9822(22)01699-2