Unihorn octopus (Scaeurgus unicirrhus)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Mollusca · Class: Cephalopoda · Order: Octopoda · Family: Octopodidae · Genus: Scaeurgus.

Accepted name: Scaeurgus unicirrhus · Authority: (Delle Chiaje, 1841) · Taxonomic status: accepted · AphiaID: 140607.

Synonyms and superseded combinations recorded for this taxon: Macrotritopus danae (Joubin & G. C. Robson, 1929); Octopus (Macrotritopus) danae Joubin & G. C. Robson, 1929; Octopus cocco Risso, 1854; Octopus rufus Risso, 1854; Octopus unicirrhus Delle Chiaje, 1841.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=140607 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (SeaLifeBase)

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

Maximum length: 12 cm · Common length: 8 cm · Depth range: 50–800 m · Habitat zone: benthic · Vulnerability index: 10 of 100 · Fishery importance: commercial.

SeaLifeBase notes: Minimum depth from Ref. 104052. Littoral. On muddy bottom (Ref. 2082). Inhabits areas with low light levels (Ref. 106818). Associated with coralline bottoms ( Ref. 275). Capable of various color patterns, skin textures and body postures (Ref. 106818). Octopods are carnivores, preying mainly on crustaceans, fish and shelled mollusks (Ref. 96968).

Source: SeaLifeBase species summary (SpecCode 58215) — https://www.sealifebase.se/summary/Scaeurgus-unicirrhus.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

362 georeferenced occurrence records for Scaeurgus unicirrhus are published through GBIF from 16 countries or marine areas. The map above plots 78 distinct locations from a sample of 362 records, omitting 5 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: Spain (257); United States of America (55); Portugal (8); Bermuda (6); Australia (4); Brazil (3); Bahamas (3); France (3); French Guiana (3); Guadeloupe (3); Martinique (3); Cuba (2); Greece (2); Japan (1); Mexico (1).

Marine regions with a valid WoRMS distribution record: European waters (ERMS scope); Gulf of Mexico; Turkish part of the Aegean Sea; Turkish part of the Mediterranean Sea - Eastern Basin; Azores Exclusive Economic Zone.

Source: GBIF Occurrence Search (taxonKey 9385151) — https://www.gbif.org/occurrence/search?taxon_key=9385151&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=140607 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Description and natural history (Wikipedia)

S. unicirrhus has an oval, muscular body with a mantle length reaching up to 12 cm and arms extending to about 40 cm. The skin shows irregular papillae that provide camouflage on sandy or rocky bottoms. A distinctive characteristic is the single cirrus above each eye-hence the name "unicirrhus". Members of this genus possess two rows of suckers, a skin keel around the body margin, and males have the hectocotylus on the third left arm, unlike most other octopus species where the modified arm is the third right.

According to Norman (2000), the species is typically reddish-brown, with robust arms and a tendency to inhabit soft substrates.

The genus Scaeurgus was described by Alcide d'Orbigny in 1840, who designated S. unicirrhus as its type species. Subsequent revisions confirmed S. unicirrhus as the only Mediterranean representative of the genus. Three additional species: S. patagiatus, S. tuber and S. jumeau are known from the Pacific Ocean.

Scaeurgus unicirrhus occurs throughout the Mediterranean Sea and along the eastern Atlantic coast from Portugal and the Azores to North Africa and southward to Senegal. It inhabits sandy, muddy or rubble substrates between 30 and 600 m of depth, sometimes occurring on hard bottoms. The species is primarily nocturnal and shelters in crevices, empty shells, or under stones during the day.

In the Azores Archipelago, S. unicirrhus was first reported in a regional synopsis of the local Octopoda fauna. Specimens were collected on upper-slope habitats, mostly between 200 and 600 m. FAO (2016) also lists the species among confirmed Atlantic records around oceanic islands.

In the Madeira Archipelago, the species was documented through additional records expanding the cephalopod fauna of the region. The Madeiran material derives from upper-slope environments similar to those of the Azores, suggesting continuity across the Macaronesian islands.

Scaeurgus unicirrhus is a benthic predator feeding mainly on crustaceans, bivalves, gastropods and occasionally small fish. It may bury itself partially and ambush prey. Females produce small eggs, approximately 3 mm in diameter, attaching them within sheltered cavities. They brood the eggs until hatching, after which planktonic young emerge.

The species likely has a biennial life cycle, with spawning occurring in spring and early summer.

S. unicirrhus is a relevant species for studies of cephalopod evolution and adaptation to deep-sea environments. Its wide distribution across the Mediterranean and eastern Atlantic makes it a useful biogeographic indicator. FAO (2016) provides detailed taxonomic keys, distribution data, and anatomical drawings for accurate identification.

Source: Wikipedia: Scaeurgus unicirrhus — https://en.wikipedia.org/wiki/Scaeurgus_unicirrhus (CC BY-SA 4.0). Accessed 2026-09-23.

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