Erronea onyx, common name the onyx cowry, is a species of sea snail, a cowry, a marine gastropod mollusk in the family Cypraeidae, the cowries.^[1]

Quick Facts Erronea onyx, Scientific classification ...

Erronea onyx
Five views of a shell of Erronea onyx
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subclass:	Caenogastropoda
Order:	Littorinimorpha
Family:	Cypraeidae
Genus:	Erronea
Species:	E. onyx
Binomial name
Erronea onyx (Linnaeus, 1758)
Synonyms[1]
Cypraea onyx Linnaeus, 1758 (basionym) Cypraea pulla Gmelin, 1791 Cypraea prunus Röding, 1798

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The shells of these quite common cowries reach on average 32–38 millimetres (1.3–1.5 in) of length, with a minimum size of 24 millimetres (0.94 in) and a maximum size of 57 millimetres (2.2 in). The dorsum surface of Erronea onyx is smooth, shiny and generally golden brown, with alternating longitudinal fuzzy bands of translucent bluish and reddish colors (hence the Latin name onyx). The base and the margins are dark brown or black, sometimes the teeth are orange. In the living cowries mantle is dark brown, quite thin, with bluish papillae.

This species occurs the Indian Ocean on the coasts of Aldabra, the Comores, Kenya, Madagascar, Mauritius, Mozambique, Réunion, the Seychelles, Tanzania and in the Pacific Ocean along East China, Thailand, northern Australia, Indonesia, Philippines, Palau Islands and Solomon Islands.

Erronea onyx lives in tropical and subtropical zones, in shallow subtidal water up to 5–25 metres (16–82 ft) depth, mainly in muddy areas or sandy sea floor, feeding on algae or coral polyps.

What used to be called Erronea onyx adusta, Lamarck, 1810 is now accepted as Erronea adusta.^[2]