May the fourth be with you: the Arctic sand star

Whether you're a George Lucas superfan or can't tell a Wookie from a Wampa, you have to admit, Star Wars is a pop culture phenomenon. And doesn't the Arctic sand star just sound like a creature you would find on the planet Tatooine? Let's "dig in" and find out what makes this earthly asteroid a force of nature in sediment communities around the globe.

Long ago, in a mud sample far, far away…

The Arctic sand star, Leptychaster arcticus, is even more of a hermit than Obi-Wan Kenobi. There is very little information out there about its life history, mostly because these stars generally inhabit the dark expanse of the Outer Rim Territories (a.k.a. the deep sea), where they avoid the prying eyes and snapping benthic grabs of researchers. They inhabit muddy, sandy and pebbly bottoms in depths up to 2,400 meters (almost 8,000 ft!) and are uncommon to see in the shallows. The single small specimen collected in Puget Sound by our program (way back in 1989) was found in Samish Bay, at a depth of only 21 meters - likely a youngling attempting to make its way to deeper water.

The Arctic sand star's geographic range spans the Earth's Arctic circumpolar region, reaching only about as far south as Nova Scotia and Ireland in the Atlantic Ocean, to Japan and Oregon on either side of the Pacific.

Come to the dark side

Sea stars have two sides, and I'm not talking about good and evil. A sea star's aboral (top) side is generally covered with protective spines, and the oral (bottom) side contains rows of tube feet with the mouth arranged in the center.

On an Arctic sand star, the orange or pink aboral side is covered with prominent spike bunches called paxillae. Around the edges of the star are distinct marginal plates with a grainy texture. On the oral side, three- to four-toothed furrow spines line each of the star's five ambulacral grooves. These channel-like grooves house the tube feet and the water vascular system. Instead of a circulatory system, sea stars use water to move oxygen, food, and waste through their bodies. Even bloodless and heartless, they are still likeable - unlike the Galactic Empire!

Use the force

Many sea stars can force one of their two stomachs out through their mouth to digest food outside the body before bringing it into their second, internal stomach to finish the job. This Jabba the Hutt-esque talent allows the stars to consume larger prey than they would normally be able to fit into the tiny mouth on their underside, and has given them a reputation as important predators in benthic communities worldwide.

Researchers in eastern Canada were curious to know if the same held true for species living at great depths, including the Arctic sand star. The specimens they collected had highly expandable stomachs engorged with sediment, leading them to conclude that this species is a specialized infaunal mud ingester rather than a terrifying Death Star. Arctic sand stars lie buried, swallowing mouthfuls of mud and sand and filtering out tiny animals like foraminifera and mollusks. This behavior has the potential to make them an influential force on local sediment and nutrient conditions.

I am your father

Arctic sand stars belong to a small group of sea stars known for their specialized parental care. Instead of releasing their young into the universe to fend for themselves, the mother stars carry them around on their aboral surface, where the spiky paxillae protect them from potential predators.

Once the young Arctic sea stars outgrow their mom's protective embrace, they strike out on their own. As adults, they probably won't face as much danger as their shallow water counterparts - the deep sea has fewer animals, including sea star predators. But if they happen to lose a limb in a chance encounter with, say, a Sith Lord, they can grow it right back through a process called regeneration.

A new hope

In 2024, researchers analyzed the complete genome (or DNA) of Arctic sand stars, something that has rarely been done with deep-sea organisms because of the difficulty in collecting them. Leptychaster arcticus is the first species of its genus to be studied in this way.

Every new DNA sequence added to global genetic libraries assists taxonomists with identifications and makes it easier to detect and describe new species, understand evolutionary relationships, and develop better strategies for preventing biodiversity loss. We consider that a win for the rebel forces fighting to protect our marine ecosystems!

About the Critter of the Month series

Dany Burgess is a benthic taxonomist, a scientist who identifies and counts the sediment-dwelling organisms as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see to detect changes over time and understand the health of Puget Sound.

Dany shares her discoveries by bringing us a benthic Critter of the Month. These posts 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.