Ophiura sarsii
A cold-water brittle star abundant in Arctic and Sub-Arctic seas.
**Ophiura sarsii**, commonly called the notched brittle star, is a cold-water, bottom-dwelling marine species that lives in the Arctic and Sub-Arctic seas. It was first described by Christian Frederik Lütken in 1855. These brittle stars are typically red or brown, grow to a large size, and are very numerous in their habitats. They can survive for as long as 27 years.
**Morphology** Adults have arms that reach up to 90 millimeters in length, which is about three to four times the diameter of the central disk. The disk itself is usually up to 25 millimeters across, though it can be as wide as 40 millimeters. It is rigid and heavily calcified—much larger than the disk of *Ophiocten sericeum*, a similar cold-water brittle star that shares the same environment and maxes out at 18 millimeters. As *O. sarsii* leaves its larval stage, the disk becomes pentagonal with small holes. Over time, it develops spines, arms, arm joints, and protective plates.
**Growth** This brittle star can live up to 27 years. Studies show it goes through an eight-year period of fast growth, followed by four to five years with no growth, and then another fast-growth phase until death. Growth is measured using bands on the disk.
**Habitat** *O. sarsii* is found in the northern Atlantic and Pacific Oceans, as well as throughout the Arctic Ocean. It lives mainly in the bathyal zone of the open ocean, sometimes covering up to 96% of the seabed. In the Arctic, it prefers slopes and shelves with soft bottoms. It outnumbers all other brittle star species in its habitat, making up 71% of the benthic and epibenthic brittle stars in the Arctic Ocean.
**Diet and feeding habits** *Prey*: Though mostly carnivorous, *O. sarsii* is a trophic generalist. Its primary food is amphipods, but it also eats arthropods, molluscs, cnidarians, and annelids. Its diet is heavily focused on the amphipod families Ampeliscidae and Lysianassidae, which made up 54–70% of stomach contents in a study by Harris et al. (2009).
*Predators*: Benthic carnivorous fish and crabs prey on *O. sarsii*. It is the main food of the American plaice in the Gulf of Maine; one study by Packer et al. (1994) found that 82% of plaice gut contents were ophiuroids, with 65% of those being *O. sarsii*. More than half of adult red king crabs also eat brittle stars like this one.
Quick Facts
- Genus
- Ophiura
- Species
- sarsii
Facts from the source article.
Lore & Background
Ophiura sarsii was discovered by Christian Frederik Lütken in 1855. Adults have arms that can extend up to 90 millimeters, or 3-4 times the disk size, and their central disks are commonly up to 25 millimeters in diameter but can reach 40 millimeters. The disk is rigid and heavily calcified, much larger than the similar species Ophiocten sericeum, which has a maximum disk size of 18 mm. As it transitions out of its larval stage, the central disk becomes a pentagonal shape with small perforations, and it later gains spines, arms, arm joints, and protective plates.
This species can live for up to 27 years, with an 8-year period of fast growth followed by a 4-5 year period of no growth, then another period of fast growth until death. Growth can be measured using growth bands on their disks. They are found in the northern Atlantic and Pacific Oceans, as well as the entire Arctic Ocean, primarily in the bathyal zone on soft sediment. In some areas, they cover as much as 96% of the seabed and outnumber all other brittle star species, making up 71% of the abundance in the benthic and epibenthic parts of the Arctic Ocean.
Reader's Guide
Ophiura sarsii is significant as a dominant benthic species in Arctic and Sub-Arctic ecosystems, both as a trophic generalist feeder and as primary prey for larger fish and crabs. Its diet consists mostly of amphipods, particularly from the families Ampeliscidae and Lysianassidae, which made up 54-70% of stomach contents in a study by Harris et al., 2009. It is the main prey of the American Plaice in the Gulf of Maine, with one study by Packer et al. (1994) finding that 65% of ophiuroids in their gut were O. sarsii. Over 50% of adult red king crabs also consume brittle stars like O. sarsii.
A study by Dvoretsky & Dvoretsky, 2021 found that O. sarsii and other deep sea echinoderms colonize red king crabs in the Barents Sea, possibly to avoid predation, though infestations occur in only 0.7-1.1% of crabs. Human usage includes extraction of sulfated steroidal polyols from fresh tissue, which may be used for anti-HIV medication, and THA from their limbs for anti-inflammatory and anti-allergenic substances. Climate change has caused a decrease in growth and biomass, especially in the Yellow Sea, and may cause protein unfolding in their DNA, though a subspecies studied by Liao et al., 2025 may regulate gene expression to combat these effects.
Did You Know?
- They can live for up to 27 years, with an 8-year fast growth period followed by a 4-5 year no-growth period.
- In the Arctic Ocean, they make up 71% of the abundance in benthic and epibenthic zones.
More in Sea Cucumbers and Brittle Stars, Part 3 1-24
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