Atheraster umbo
Deep-sea starfish with stout body and abundant pedicellariae.
Atheraster umbo is a deep-sea starfish belonging to the family Goniasteridae, first formally described by Christopher Mah in 2026. Its body is robust and strongly star-shaped, with arms about 3.2 times longer than the width of the central disk. The arms are long and triangular, and the curves between them (interradial arcs) range from slightly curved to straight.
The upper (abactinal) surface is covered with irregular, bare plates that continue all the way to the arm tips. On the arms, these plates vary from flat to strongly convex and are noticeably larger than the plates on the central disk. Pincer-like structures called pedicellariae are plentiful, with 4 to 12 of them sitting inside a depression in each interradius.
Along each side of an arm, there are 20 to 22 marginal plates, totaling 40 to 44 per interradius. In the interradial areas, these plates are mostly smooth and bare except for 2 to 10 small granules or tubercles. On the arms themselves, each marginal plate has a single raised, knob-like projection (tumescence). Coarse, almost tubercular granules are most common on the interradial marginal plates—ranging from 1 to 15—but become fewer and eventually absent along the arm surface.
On the underside (actinal surface), the plates have distinct alveolar pedicellariae, each flanked on both sides by split hemispherical granules. Furrow spines number between 5 and 15, most often 7 or 8. Each adambulacral plate bears a single, prominent tong-like pedicellaria with square (quadrate) valves, accompanied by a large, thick subambulacral spine that is 2 to 3 times thicker than the furrow spines and set at an oblique angle. Each oral plate has a large, paddle-shaped pedicellaria, giving two per interradius, though they are not symmetrically placed.
This species has a wide distribution across the South Pacific and Indian Ocean, with documented records from New Caledonia, Tasmania, Lord Howe Island, and the Cocos (Keeling) Islands. It is a deep-sea starfish, found at depths between 1,589 and 1,896 metres (5,213 to 6,220 feet).
Quick Facts
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- Atheraster umbo
Facts from the source article.
Lore & Background
Atheraster umbo was first described by Christopher Mah in 2026. Its body is stout and strongly stellate, with an arm-to-disk ratio of approximately 3.2. The arms are elongate and triangular, with weakly curved to straight interradial arcs. The abactinal (upper) surface is covered in irregular, bare plates that extend to the arm tips; plates on the arms are variably flat to strongly convex and acutely large relative to adjacent plates on the central disk. Pedicellariae (pincer-like structures) are abundant, with 4–12 situated within a depression in each interradius.
There are 40–44 marginal plates per interradius (20–22 per side of an arm). On the interradial areas, these plates bear 2–10 small granules or tubercles but are otherwise smooth and bare. Along the arms, each marginal plate features a single distinct tumescence—a raised, knob-like projection. Coarse, nearly tubercular granules are most abundant (1–15) on the interradial marginal plates, decreasing in number and becoming absent along the arm surface. On the actinal (under) surface, the plates display distinct alveolar pedicellariae, each flanked on either side by bisected hemispherical granules. Furrow spines number 5–15, most commonly 7 or 8. Each adambulacral plate bears a prominent, single, tong-like pedicellaria with quadrate valves, accompanied by a large, thick subambulacral spine that is 2–3 times the thickness of the furrow spines and set at an oblique angle. Each oral plate possesses a large, paddle-shaped pedicellaria, resulting in two per interradius, though these are not symmetrically positioned.
Atheraster umbo has a wide distribution across the South Pacific and Indian Ocean, with documented occurrences including New Caledonia, Tasmania, Lord Howe Island and Cocos (Keeling) Islands. It is a deep-sea species found at depths ranging from 1,589 to 1,896 metres.
Reader's Guide
Atheraster umbo contributes to the understanding of deep-sea starfish diversity within the family Goniasteridae. Its description in 2026 by Christopher Mah adds a new species to the known fauna of the South Pacific and Indian Ocean. The species is characterized by a stout, strongly stellate body with an arm-to-disk ratio of approximately 3.2, and its abactinal surface features irregular bare plates with variable convexity. The presence of abundant pedicellariae—4–12 per interradius—and distinct marginal plate tumescences along the arms are key morphological traits. The actinal surface shows alveolar pedicellariae flanked by bisected hemispherical granules, and furrow spines typically number 7 or 8. The subambulacral spine is notably thick, 2–3 times the thickness of furrow spines, and set at an oblique angle. The species' wide distribution across New Caledonia, Tasmania, Lord Howe Island and Cocos (Keeling) Islands, at depths of 1,589 to 1,896 metres, highlights its ecological range in deep-sea environments. Its paddle-shaped oral pedicellariae, though asymmetrically positioned, further distinguish it within its genus.
Frequently Asked Questions
Who is Atheraster umbo?
Atheraster umbo is a stout, deep-sea starfish classified in the family Goniasteridae. It was given its formal scientific name by Christopher Mah in 2026, making it a relatively new addition to the taxonomic record.
What does Atheraster umbo look like?
It presents a bold five-pointed star shape with long, triangular arms that stretch to roughly 3.2 times the diameter of the central disk, and the arcs between the arms can be gently curved or almost perfectly straight. The upper surface is armored with irregular, soft-tissue-free plates that run continuously to the arm tips, and the plates on the arms are visibly larger and more domed than those on the disk.
Where does Atheraster umbo live?
This species is confined to the deep ocean, with records falling between approximately 1,589 and 1,896 metres (5,213–6,220 ft) below the surface. No shallow-water or coastal occurrences have been reported.
Who first described Atheraster umbo and when?
Christopher Mah formally introduced the species to the scientific literature in 2026. Before that publication, the animal had no established name in the taxonomic record.
What sets Atheraster umbo apart from its Goniasteridae relatives?
It carries an unusually high number of marginal plates—40 to 44 per interradius, or 20 to 22 along each side of a single arm—and its furrow spines range from 5 to 15, with 7 or 8 being the most common count. Combined with its abundant pedicellariae and the oversized, strongly convex arm plates, these traits make it easy to pick out within the family.
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