Bobbing along in ocean currents a half mile below the surface is a worm like no other.

Our team first spotted the unusual pigbutt worm (Chaetopterus pugaporcinus) in 2001 and had a tough time determining how to categorize such a curious critter. Working closely with our collaborators, we eventually confirmed we had encountered a new species of bristle worm that drifts through the midwater instead of living on the seafloor.

But studying the pigbutt worm was no trivial task. 

This little worm is about the size of a hazelnut, and even using our high-resolution cameras, it took the eagle eyes of our expert biologists to spot these miniature orbs in the massive ocean. Our skilled submersible pilots were able to gently sample them and transport them back to the ship alive for detailed examination.

In the lab, we saw that Chaetopterus pugaporcinus is segmented like other bristle worms. However, the segments are highly compressed in the front and back ends, while the midsection is greatly inflated, probably to help keep the animal afloat. Sequencing the pigbutt’s DNA established that they fit into the family Chaetopteridae. Members of this group of worms typically live attached to the seafloor in parchment-like tubes, although they do have a free-swimming larval stage. The mix of both larval and adult features seen in the pigbutt worm is certainly unusual.

Observing these animals up close in the lab also revealed aspects of their natural history that we were unable to see in the wild. We learned that these incredible worms are bioluminescent. They produce blue light in their body tissues as well as green glowing mucous secretions, an adaptation that may be used to deter predators.

Chaetopterus pugaporcinus casts out a web of snot to capture bits of organic material called marine snow to eat. Mucus is a useful substance for snaring food in the deep sea where it may be sparse. Numerous other animals get their nutrition this way too. Animals of all shapes and sizes in the ocean perform an essential climate service by taking up excess carbon dioxide from the atmosphere and transporting it down deep in the ocean. These assorted midwater mucous-feeders help repackage carbon to sink more rapidly to hungry seafloor communities.

Since their discovery two decades ago, we have only seen this unique worm offshore of Central California, primarily around Monterey Bay and a few observations off of the Channel Islands. The deep sea teems with life, and many remarkable species are still awaiting discovery in the dark. We are working to catalog deep-sea animals and environments so we can predict how threats like climate change and mining will affect them. The pigbutt worm is just one of more than 200 new species named by our team and collaborators. Who knows what we will find next?