Two previously unknown species of sea spider have been identified in the shallow waters of the Salish Sea, the stretch of ocean and coastal channels separating Washington State from the Canadian province of British Columbia. The discovery, made by researchers at the University of British Columbia, represents the first time sea spiders have been documented in that area in more than a century, according to the team.
The finds were made off the coast of two British Columbia islands, Vancouver Island and Quadra Island, during a collecting period that ran from September 2023 through August 2024. Both animals are tiny — roughly a centimeter across — a size that makes them easy to overlook and helps explain why a group of specialists can go more than 100 years without turning up anything new in a place they study regularly.
The effort falls into a class of animals scientists call Pycnogonida. Sea spiders are marine arthropods, meaning they are distant relatives of insects, crabs and other creatures with jointed, segmented bodies. According to the researchers, scientists have identified more than 1,300 species of sea spiders to date, and the group remains an active frontier of discovery.
Cormac Toler-Scott, the lead researcher on the UBC team that described the new species, told NPR that the resemblance between sea spiders and land spiders is not a coincidence. Some species, he said, not only look like their eight-legged terrestrial counterparts but are actually related to them. The visual similarity, however, conceals a fundamentally different way of life.
"They never made that transition to land," Toler-Scott said, pointing to the fact that sea spiders stayed in the water while the lineage that produced familiar land spiders and other arachnids moved ashore. "They really need to be in the water. They're quite slow moving. They just kind of crawl on the seafloor."
That lifestyle shapes everything about them. Slow, steady movement along the bottom means a very different set of demands from those faced by a spider running across a wall or a web, and the anatomy of the new species reflects that. One of the two animals, named *Callipallene pilosuspedes*, has red eyes, a three-lipped mouth shaped like a triangle and a curved spine that covers its legs.
The most striking feature of *Callipallene pilosuspedes* is a set of appendages that emerge from the animal's belly rather than its head or thorax. These are called ovigers, and they can be used to groom the animal and comb dirt away from its body. In a creature that spends its life crawling through seawater along the seafloor, that kind of self-cleaning apparatus is a practical necessity rather than a luxury.
The second new species, *Tanystylum kiixin*, was photographed with round eggs visible inside its legs — a reproductive strategy in which a female carries developing young on her own body, guarding them by staying in place rather than dispersing them into the current. Photographs of the specimen credited to Cormac Toler-Scott and the University of British Columbia show the pale, spindly animal with clusters of round eggs held close to its limbs.
For marine taxonomists, the timing of the collections matters as much as the specimens themselves. A collecting window of nearly a year means researchers returned to the same shallow ground across a full seasonal cycle, encountering animals that may be present only during certain months or conditions. Building such a series also allows scientists to compare the range of variation within a population, a key step in confirming that a specimen truly belongs to a new species rather than an unusual individual of a known one.
The Salish Sea itself is a distinctive environment: an inland marine system threaded through a network of islands and channels, with tides, currents and shifting salinity conditions. For a group of animals that Toler-Scott described as slow and firmly tied to the water, the region offers a range of shallow habitats in which sea spiders can move slowly along the bottom. The Strait of Georgia waters between Washington and Vancouver Island are among the areas covered by the collections.
The previous absence of any recorded sea spiders from the area, despite the surrounding waters being comparatively well studied, has prompted researchers to look more closely at historical collecting records. A gap of 100-plus years in a record for a recognizable and, by the standards of marine invertebrates, conspicuous animal suggests that either the animals were overlooked or the earlier work simply did not include the habitats they occupy.
The broader implication is that the sea spider family is still incompletely known. With more than 1,300 species identified and additional collecting continuing in shallow coastal zones like the Salish Sea, the pace of discovery suggests the total count will keep climbing. Every new description also adds to a growing picture of an ancient lineage that stayed in the ocean, diverged from its land-based relatives and then quietly persisted in habitats where small, slow animals are easy to miss.
The two new species are being described from material collected between September 2023 and August 2024 off the islands of Vancouver and Quadra, and they join a roster of sea spider species still being added to the scientific record. For the Salish Sea, the finding closes a century-long gap in the local list. For scientists studying the animals themselves, it is a reminder that even in familiar waters, a group they thought they knew remains full of surprises.
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