Striped bum coral (Heterocyathus aequicostatus)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Cnidaria · Class: Hexacorallia · Order: Scleractinia · Family: Caryophylliidae · Genus: Heterocyathus.

Accepted name: Heterocyathus aequicostatus · Authority: Milne Edwards & Haime, 1848 · Taxonomic status: accepted · AphiaID: 216146.

Synonyms and superseded combinations recorded for this taxon: Brachytrochus simplex Duncan, 1876; Heterocyathus aequicostatus carthausi Felix, 1913; Heterocyathus aequicostatus delicatus Sakakura, 1935; Heterocyathus aequicostatus elberti Felix, 1913; Heterocyathus cochlea (Spengler, 1781); Heterocyathus elongatus Hu, 1987; Heterocyathus lamellosus (Verrill, 1865); Heterocyathus oblongatus Rehberg, 1892; Heterocyathus philippensis Semper, 1872; Heterocyathus philippinensis Semper, 1872; Heterocyathus rembangensis Gerth, 1921; Heterocyathus roussaeanus Milne Edwards & Haime, 1848; Heterocyathus rousseaui (Haime & Milne Edwards, 1857); Heterocyathus sandalinus Gerth, 1921; Heterocyathus woodmasoni Alcock, 1893; Heteropsammia aequicostatus (Milne Edwards & Haime, 1848); Psammoseris rousseaui Milne Edwards & Haime, 1851; Stephanoseris rousseaui Milne Edwards & Haime, 1851.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=216146 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (SeaLifeBase)

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

Depth range: 0–40 m · Habitat zone: reef-associated.

SeaLifeBase notes: Free-living, solitary corals with a flat base. Commonly occurs on soft horizontal substrates at 20 m or more. Only at night do polyps extend. Associated with other corals, Heteropsammia cochlea and Cycloseris cyclolites (Ref. 3477).

Source: SeaLifeBase species summary (SpecCode 46317) — https://www.sealifebase.se/summary/Heterocyathus-aequicostatus.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

304 georeferenced occurrence records for Heterocyathus aequicostatus are published through GBIF from 26 countries or marine areas. The map above plots 92 distinct locations from a sample of 304 records, omitting 17 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: Australia (57); Réunion (56); Philippines (47); Mexico (29); New Caledonia (21); Indonesia (19); Japan (19); India (7); Chinese Taipei (7); Mozambique (6); Iran (Islamic Republic of) (4); Maldives (4); Congo, Democratic Republic of the (3); Fiji (3); Myanmar (3).

Marine regions with a valid WoRMS distribution record: Seychelles; Indo-West Pacific; Réunion Exclusive Economic Zone; Myanmar Exclusive Economic Zone; Indian Exclusive Economic Zone; Yemeni Exclusive Economic Zone; Maldives Exclusive Economic Zone; Philippine Exclusive Economic Zone; Japanese Exclusive Economic Zone.

Source: GBIF Occurrence Search (taxonKey 8086695) — https://www.gbif.org/occurrence/search?taxon_key=8086695&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=216146 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Conservation status (IUCN Red List)

The IUCN Red List assesses Heterocyathus aequicostatus Milne Edwards & Haime, 1848 as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 133431) — https://www.iucnredlist.org/species/133431/0; GBIF IUCN Red List category endpoint (taxonKey 8086695) — https://api.gbif.org/v1/species/8086695/iucnRedListCategory. Accessed 2026-09-23.

Description and natural history (Wikipedia)

Heterocyathus aequicostatus is a small, solitary, free-living coral with a flat base. The polyp sits in a roughly circular corallite (stony cup) which has up to four cycles of toothed septa (stony ridges) radiating from it, making 48 septa in total. These continue over the rim of the corallite as prominent costa (ridges) down to the smooth, flat base. This coral grows to a maximum diameter of 1.5 cm and is a pale brown colour, often with a pale green oral disc.

Heterocyathus aequicostatus is native to the tropical and sub-tropical Indo-Pacific region, its range extending from Madagascar and the Arabian Peninsula to Indonesia, Australia, the Philippines and Japan. It is found at depths of at least 20 m and sometimes down to 100 m on level or gently sloping sandy or gravelly shelves between reefs.

This coral sometimes harbours photosynthetic, single-celled dinoflagellates called Zooxanthellae in its tissues. The polyps extend their tentacles at night to feed, normally remaining retracted by day. The larvae are planktonic, and when fully developed they are attracted to settle on the shells of tiny gastropod molluscs, gradually enveloping the molluscs as they grow into juvenile corals.

In Australia, this coral often lives in symbiosis with the sipunculid worm, Aspidosiphon muelleri. The worm often has an entrance hole on the oral disc through which it can extend its introvert to feed. Another hole in the base of the coral is used by the worm to move the coral about on the sandy seabed, preventing the coral from becoming buried.

In general coral reefs are being degraded, and although this coral is a common species, it is likely that its populations are in decline along with their habitats. The International Union for Conservation of Nature has listed H. aequicostatus as being of "least concern" as it considers that the rate of decline in its populations is not sufficient to justify listing it in a more threatened category.

Source: Wikipedia: Heterocyathus aequicostatus — https://en.wikipedia.org/wiki/Heterocyathus_aequicostatus (CC BY-SA 4.0). Accessed 2026-09-23.