On Caribbean coral reefs, an unlikely partnership has gone largely unnoticed: Tiny fish regularly nestle within the feathery structures of tube worms. While these sensitive worms typically snap shut at the slightest disturbance, they show a remarkable tolerance for their tiny guests.

A study published in Symbiosis found that these small coral reef fish form previously undocumented associations with Christmas tree worms and other tube-dwelling worms on Caribbean coral reefs. This discovery is potentially the first time this symbiotic behavior has been observed between fish and worms.