Eyes Under Puget Sound: Critter of the Month – The Pacific Stinkworm

Making a stink

Compared to most of the tiny mud-dwelling invertebrates in Puget Sound, this month’s critter, the Pacific Stinkworm, is a giant — and it has a gigantic stench to match.

Kingdom, Animalia; Phylum, Annelida; Class, Polychaeta; Order N/A; Family, Travisiidae; Genus, Travisia: T. pupa

Vampire-free zone

Travisia pupa may look unassuming, but like other species of marine segmented worms in its genus, it has a hidden talent that will knock your socks off. When disturbed, the stinkworm, as its name suggests, gives off a pungent odor similar to rotting garlic.

Our scientists recently witnessed this firsthand while sampling the sediments in Admiralty Inlet. We immediately knew we had scooped up a stinkworm because of the terrible stink it emitted as the benthic grab landed on the deck of the boat. It certainly does the trick as a human (or vampire) repellent!

Although this pungent phenomenon is not well-studied, it is generally thought to be a chemical defense mechanism used to deter predators. There has also been speculation by scientists that the smell is a byproduct of microbial fermentation in the gut of Travisia — that is, the worms use symbiotic bacteria in their digestive systems to help obtain nutrients from their food.

A great face for radio

Travisia pupa is conspicuous on muddy ocean bottoms from Alaska to Mexico, growing to the whopping size of 8 cm long (a little over 3 inches) and 3 cm wide. With its fat, grub-like body and covering of wart-like vesicles, it’s not likely to win any beauty contests, but we think it might qualify for Miss Congeniality.

Pointy end has a hole in it. The animal is wrapped in pink and white ridges. White gaps with pink things, like bent tongues, stick out.

Close-up of the underside of the head, showing the mouth.

In addition to the unflattering moniker “stinkworm,” T. pupa is also referred to as the Pupa Utility Worm, which says a bit more about its admirable qualities. “Pupa” potentially comes from the strong resemblance to the stage in a butterfly’s life when it is undergoing metamorphosis. “Utility” refers to its beneficial role as a bioturbator, performing the important ecological function of turning over and aerating the sediment. T. pupa accomplishes all of this while deposit feeding — burrowing through the sediment, ingesting mud and food particles alike.

Warts and all

Left looks like a pink potato bug with red legs; the closeup indicates one of the ridges: “vesicle” and one little tongue: “branchia.”

LEFT: Live Travisia pupa, ventral (bottom) view; Photo by the BIO Photography Group, Biodiversity Institute of Ontario (CreativeCommons)
RIGHT: Close-up of the body, showing branchiae and vesicles.

Puget Sound is actually home to four species of Travisia, but picking out T. pupa is a snap thanks to its vesicles, small fluid-filled sacs which occur in several different sizes along its body. The three other species that occur in Puget Sound have smaller vesicles that are all the same size. All four species have branchiae (breathing structures or gills) along the length of their bodies; in life these are bright red.

Critter of the Month

Our benthic taxonomists, Dany and Angela, are scientists who identify and count the benthic (sediment-dwelling) organisms in our samples as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see in order to understand the health of Puget Sound and detect changes over time.

Dany and Angela share their discoveries by bringing us a Benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.