Scientists discovered two bizarre new sea spiders that are “nightmare fuel”

The discoveries mark the first new sea spider species formally described from the Salish Sea in nearly 100 years. Published in Organisms Diversity & Evolution, the study combines detailed physical observations with genetic analysis to help fill major gaps in scientists' understanding of these unusual marine animals.

"I was interested in how sea spiders are impacted by climate change and human disturbance, because marine invertebrates in the Salish Sea are particularly at-risk, and I couldn't find anything," said lead author Cormac Toler-Scott, who conducted the work as part of his master's degree in zoology at UBC. "That's largely because people don't know much about what species exist here and what their lifestyle is."

According to Toler-Scott, that lack of basic information affects many marine arthropods. "In order to understand how marine invertebrates are being impacted by things like climate change and how we can better protect these key elements of the ecosystem, we have to be able to identify them."

Ancient Animals With Bizarre Biology

Sea spiders belong to an ancient lineage that arose roughly 500 million years ago. They are related to spiders, scorpions, and horseshoe crabs, but unlike their land-dwelling relatives, they remained entirely marine.

Their appearance is strange even by arthropod standards. Some species can have as many as 12 legs, along with a sucking proboscis used for feeding. Their size varies dramatically, from less than a centimeter long to more than 70 cm in Antarctica, where some species hunt smaller animals in deep ocean environments.

"They've retained some weird traits," said Toler-Scott. "A lot of the shallow water species are quite small, and so they'll live as parasites on larger organisms, and they use this weird apparatus called a proboscis to suck the juices out of their host."

Sea spiders also have several unusual reproductive and physiological traits. They breathe directly through their skin, and males take responsibility for carrying and raising the young.

Females have ovaries that extend through their limbs, where eggs develop before 'popping out' through a dedicated pore. During mating, the male collects the eggs using specialized appendages near the base of his head called 'ovigers'. He coats the eggs with glue secreted from his legs and attaches clusters of egg sacs to his own body while they develop.

Hairy Feet, Red Eyes, and a Strange Mouth

Researchers collected the newly described species between September 2023 and August 2024 during dives reaching depths of up to 18 meters. Specimens came from a variety of marine habitats around Quadra Island, Vancouver, Bamfield, and Victoria.

One of the species was named Callipallene pilosuspedes because of the long, curved spines covering the lower portions of its legs. The name is a reference to the Latin words for 'hairy feet'.

Its appearance is especially distinctive. The animal has red eyes and a short proboscis equipped with claws that help it grab food before biting. Its mouth is triangular, divided into three lips, and surrounded by sensory tendrils, giving it an appearance reminiscent of a tiny marine Sarlacc pit.

The species also has unusually agile ovigers that serve another purpose beyond carrying eggs. Under a microscope, researchers watched the sea spider wrap these appendages around its legs and use comb-like spines to groom and clean its body.

Despite its memorable appearance, the team found only a single specimen.

A Sea Spider Covered in Parasites

The second newly described species, Tanystylum kiixin, takes its name from an ancient Indigenous village site near the location where specimens were first collected.

Pronounced 'kee-hin', the name refers to the sound of waves crashing at the base of the village site.

Unlike Callipallene pilosuspedes, this species has much smaller and less flexible egg-carrying limbs. That appears to limit its ability to groom itself effectively.

Researchers often found dirt and debris clinging to the animals, along with tiny parasites living on their bodies. The result is what Toler-Scott describes as "an ecosystem within an ecosystem within an ecosystem."

DNA Reveals Hidden Sea Spider Diversity

The study is the first comprehensive investigation of Salish Sea sea spiders to combine detailed imaging with DNA analysis.

As part of the work, researchers generated genetic sequences for several species that had never been sequenced before. The team also produced an identification guide to help scientists distinguish sea spider species found throughout the region.

Both newly discovered species have now been registered in a global database, but Toler-Scott says the Salish Sea likely contains additional species that have yet to be documented.

"I only had one field season, but there's definitely more diversity out there that we haven't documented."

In other words, the Salish Sea may still be hiding plenty of additional nightmare fuel.

This research was funded by National Sciences and Engineering Research Council of Canada.