Abatus agassizii is a species of sea urchin of the family Schizasteridae.

[3] The Abatus agassizii has a twice-looped digestive system that's three times as long as the given species individual itself.

The species is a deposit-feeder, which means it relies on the consumption of the sediment it stays burrowed in.

The system is made up of several regions: the buccal cavity, anterior esophagus, posterior esophagus, anterior stomach, posterior stomach, intestine, and rectum.

Because of the low-complexity of the agassizii's diet, it is proposed that this long digestive tract holds a diverse gut microbiota.