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.

The researchers noted that the nature of the relationship between the fish and worms is unclear