Two New Sea Spider Species Turn Up in the Salish Sea — the First in Generations

CONTENTS: A team of researchers working in Canadian waters has documented two species of sea spider that scientists had never described before. The animals were found in shallow water in the Salish Sea, the body of water that separates Washington State from the British Columbia coast, marking the first discovery of a new sea spider species in that stretch of coastline in more than a century.

According to the research team, which is based at the University of British Columbia, the specimens were collected between September 2023 and August 2024, at sites off the islands of Vancouver and Quadra in British Columbia. Both of the newly described animals measure roughly a centimeter across their bodies — small even by the standards of the many-legged marine invertebrates that live on the seafloor.

Cormac Toler-Scott, the lead researcher on the team that made the discoveries, said the animals are relatives of the spiders people know from gardens and basements, and that some sea spiders even look the part, with eight legs and a compact body. But the resemblance, he said, is largely a visual one. "They never made that transition to land," Toler-Scott said. "They really need to be in the water. They're quite slow moving. They just kind of crawl on the seafloor."

For that reason, the headline finding is not likely to set off any alarm among people who dislike spiders. These animals live in the ocean and move at a pace that would make them easy to overlook, drifting or crawling along the bottom rather than scuttling across a floor or wall. Their presence in shallow coastal water also places them within reach of harbors, beaches and nearshore habitats that researchers routinely survey.

Sea spiders are marine arthropods, the same broad group that includes crabs, shrimp and lobsters, and they belong to a class scientists call *Pycnogonida*. Despite their name and their spider-like appearance, they are not true spiders, and Toler-Scott said they are related to the land-dwelling arachnids without sharing many of their habits. So far, scientists have identified more than 1,300 species of sea spiders, a number that experts generally expect to keep growing as more coastal water is sampled.

One of the two new species carries a name that reflects the physical details researchers documented: *Callipallene pilosuspedes*. According to the researchers, it has red eyes, a mouth made of three lips that is shaped like a triangle, and a curved spine that extends over the top of its legs. Like other members of its class, it grows a set of smaller limbs from the underside of its body.

Those belly-borne limbs are known as ovigers, and one of their functions is grooming. In the newly described species, the ovigers can be used to comb dirt and other debris off the animal's body and legs. The appendages also play a role in reproduction, a feature that was visible in photographs of at least one of the new species.

The second new species, *Tanystylum kiixin*, was photographed carrying round eggs that were visible inside its legs — a reminder that, in a sense, the animals carry their young with them. A number of sea spiders hold and tend their eggs in this manner, which keeps developing embryos attached to the parent for an extended period and lets the young hatch into a habitat that is already established.

The interval between collections, roughly a year of sampling, highlights how much of the Salish Sea remains unexamined in detail. The researchers said the two new species are the first sea spiders found in the area in more than 100 years, a gap that speaks to how sparsely nearshore habitats have been sampled for this particular group of animals.

That long gap carries implications beyond bookkeeping. Every undescribed species is a missing data point in estimates of how many kinds of life share a given stretch of ocean, and the number of known sea spider species has already passed 1,300 largely through the steady accumulation of small finds like this one. Discovering two at once in familiar-looking water underlines the point that familiar coastlines are not the same as well-documented ones.

The habitat itself raises questions. The new species were taken from relatively shallow water, places where temperature, salinity and oxygen can swing with the tides and the seasons. Slow-moving animals that cannot easily flee from a disturbance may be especially sensitive to changes in those conditions, whether from warming water, sediment runoff or other coastal pressures.

Understanding the group also depends on collections, not just sightings. Descriptions such as the ones for *Callipallene pilosuspedes* and *Tanystylum kiixin* rest on physical traits measured from preserved material — the shape of a mouth, the reach of a spine, the position of ovigers — which is why repeated sampling trips like the one that produced these specimens are essential to taxonomy.

For his part, Toler-Scott is candid about how the animals live. They need to stay in the water, and they spend their time crawling along the seafloor at a deliberate pace. It is a slow, unobtrusive way of life that can endure for a long time in a small corner of the ocean — and it is one that researchers working out of British Columbia say they have only just begun to document along this coast.

TITLE: Two New Sea Spider Species Turn Up in the Salish Sea — the First in Generations

CONTENTS: A team of researchers working in Canadian waters has documented two species of sea spider that scientists had never described before. The animals were found in shallow water in the Salish Sea, the body of water that separates Washington State from the British Columbia coast, marking the first discovery of a new sea spider species in that stretch of coastline in more than a century.

According to the research team, which is based at the University of British Columbia, the specimens were collected between September 2023 and August 2024, at sites off the islands of Vancouver and Quadra in British Columbia. Both of the newly described animals measure roughly a centimeter across their bodies — small even by the standards of the many-legged marine invertebrates that live on the seafloor.

Cormac Toler-Scott, the lead researcher on the team that made the discoveries, said the animals are relatives of the spiders people know from gardens and basements, and that some sea spiders even look the part, with eight legs and a compact body. But the resemblance, he said, is largely a visual one. "They never made that transition to land," Toler-Scott said. "They really need to be in the water. They're quite slow moving. They just kind of crawl on the seafloor."

For that reason, the finding is not likely to set off any alarm among people who dislike spiders. These animals live in the ocean and move at a pace that would make them easy to overlook, drifting or crawling along the bottom rather than scuttling across a floor or wall. Their presence in shallow coastal water also places them within reach of harbors, beaches and nearshore habitats that researchers routinely survey.

Sea spiders are marine arthropods, the same broad group that includes crabs, shrimp and lobsters, and they belong to a class scientists call *Pycnogonida*. Despite their name and their spider-like appearance, they are not true spiders, and Toler-Scott said they are related to the land-dwelling arachnids without sharing many of their habits. So far, scientists have identified more than 1,300 species of sea spiders, a number that experts generally expect to keep growing as more coastal water is sampled.

One of the two new species carries a name that reflects the physical details researchers documented: *Callipallene pilosuspedes*. According to the researchers, it has red eyes, a mouth made of three lips that is shaped like a triangle, and a curved spine that extends over the top of its legs. Like other members of its class, it grows a set of smaller limbs from the underside of its body.

Those belly-borne limbs are known as ovigers, and one of their functions is grooming. In the newly described species, the ovigers can be used to comb dirt and other debris off the animal's body and legs. The appendages also play a role in reproduction, a feature that was visible in photographs of at least one of the new species.

The second new species, *Tanystylum kiixin*, was photographed carrying round eggs that were visible inside its legs — a reminder that, in a sense, the animals carry their young with them. A number of sea spiders hold and tend their eggs in this manner, which keeps developing embryos attached to the parent for an extended period and lets the young hatch into a habitat that is already established.

The interval between collections, roughly a year of sampling, highlights how much of the Salish Sea remains unexamined in detail. The researchers said the two new species are the first sea spiders found in the area in more than 100 years, a gap that speaks to how sparsely nearshore habitats have been sampled for this particular group of animals.

That long gap carries implications beyond bookkeeping. Every undescribed species is a missing data point in estimates of how many kinds of life share a given stretch of ocean, and the number of known sea spider species has already passed 1,300 largely through the steady accumulation of small finds like this one. Discovering two at once in familiar-looking water underlines the point that familiar coastlines are not the same as well-documented ones.

The habitat itself raises questions. The new species were taken from relatively shallow water, places where temperature, salinity and oxygen can swing with the tides and the seasons. Slow-moving animals that cannot easily flee from a disturbance may be especially sensitive to changes in those conditions, whether from warming water, sediment runoff or other coastal pressures.

Understanding the group also depends on collections, not just sightings. Descriptions such as the ones for *Callipallene pilosuspedes* and *Tanystylum kiixin* rest on physical traits measured from preserved material — the shape of a mouth, the reach of a spine, the position of ovigers — which is why repeated sampling trips like the one that produced these specimens are essential to taxonomy.

For his part, Toler-Scott is candid about how the animals live. They need to stay in the water, and they spend their time crawling along the seafloor at a deliberate pace. It is a slow, unobtrusive way of life that can endure for a long time in a small corner of the ocean — and it is one that researchers working out of British Columbia say they have only just begun to document along this coast.