As
@exchemist has pointed out, there are many known anaerobic bacteria (bacteria that do not need oxygen to survive). There are even obligate anaerobes: bacteria for which oxygen is poisonous.
What is remarkable about this article is two-fold: first, that it is multicellular and an animal.
But more remarkable, to be, is the fact that it is a eucaryotic cell without mitochondria.
OK, what does that mean?
Well, bacteria are 'simple cells'. They don't have nuclei, they don't have internal organelles, their DNA is not organized via histones into complex structures, etc. Bacteria are said to be procaryotes.
Complex cells, like those in all animals and plants *do* have these structures. So the cells from this new animal are complex cells.
Next, there are two standard stages of 'respiration': The first part (kreb's cycle) does not require oxygen, is fast, but doesn't give a lot of energy. The second (electron transport chain) is slower, requires oxygen, and gives a LOT more energy out. Some bacteria work with only the Kreb's cycle. Others have both. All eucaryotes up to now have both.
The electron transport chain in eucaryotes happens in an organelle called the mitochondrion. This is the 'energy powerhouse' of these cells.
Well, this new animal has cells without mitochondria. That, to me, is shocking.