Red Sea star (Mediaster aequalis)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Echinodermata · Class: Asteroidea · Order: Valvatida · Family: Goniasteridae · Genus: Mediaster.

Accepted name: Mediaster aequalis · Authority: Stimpson, 1857 · Taxonomic status: accepted · AphiaID: 242160.

Synonyms and superseded combinations recorded for this taxon: Ophidiaster aequalis (Stimpson, 1857).

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=242160 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (SeaLifeBase)

Measured values published by SeaLifeBase for Mediaster aequalis. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 20 cm · Depth range: 15–495 m · Habitat zone: benthic · Vulnerability index: 10 of 100.

SeaLifeBase notes: Common in shallow subtidal waters on rocks, sand, gravel, shells, pebble and mud (Ref. 93256).

Source: SeaLifeBase species summary (SpecCode 49299) — https://www.sealifebase.se/summary/Mediaster-aequalis.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

240,194 georeferenced occurrence records for Mediaster aequalis are published through GBIF from 4 countries or marine areas. The map above plots 41 distinct locations from a sample of 3,000 records, omitting 26 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: United States of America (238,522); Canada (1,666); Mexico (5); Australia (1).

The full country table, WoRMS marine regions and the sampling notes are on this species' Distribution page.

Source: GBIF Occurrence Search (taxonKey 2271704) — https://www.gbif.org/occurrence/search?taxon_key=2271704&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=242160 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Description and natural history (Wikipedia)

M. aequalis has five (occasionally four or six) stumpy arms and grows to a diameter of up to 20 cm. The aboral (upper) surface is bright red while the oral (under) surface is an orangey-red. The tube feet are red. There is a row of conspicuous marginal plates along the edge of the arms on the aboral surface, and the central disc bears many flat-topped ossicles (platelike calcareous structures); these consist of a central group of granules surrounded by a ring of about twenty-five marginal granules.

M. aequalis is native to the western coast of North America, its range extending from Chignik Bay in Alaska southwards to Baja California. It often inhabits rocky substrates, at depths ranging from the low intertidal to around 500 m.

M. aequalis is both an omnivore and a predator and will scavenge for dead animals and detritus. As well as feeding on algae, it preys on tunicates (such as sea pork), sea pens, sponges, bryozoans, brachiopods and polychaete worms. In its turn it is hunted by the larger morning sun star. It can move at the rate of 40 cm per minute, which is fast for a starfish. Juvenile M. aequalis often congregate among the tubes of Phyllochaetopterus prolifica, a tube-dwelling worm, and research in Washington state has shown that the larvae are highly selective in where they settle, exclusively choosing to do so on these tubes.

Source: Wikipedia: Mediaster aequalis — https://en.wikipedia.org/wiki/Mediaster_aequalis (CC BY-SA 4.0). Accessed 2026-09-23.

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