This large chiton is often confused with Tonicella marmorea, both are northern species and subject to pressures from climate change.

In brief

• It is common only in Strangford Lough in Northern Ireland
• It can be found all year round under stones or rocks low on the shore, or by diving
• It is thought to be declining, possibly due to climate change.

Species description: This chiton reaches a length of up to 2 cm, and is broadly oval in shape, about 1.5 times as long as it is wide. The valves are glossy and smooth, and may have some faint growth rings apparent. They also have a distinct beak and some sculpturing is apparent. The valves are usually coloured light red to orange, but can be green-brown, orange to red-brown, with white or off-white marbling. The girdle is covered in spherical granules, which can give it a 'sandy' or 'grainy' appearance. It is also fringed with spines and usually coloured similarly to the valves (light red to orange but can be orange - red-brown) with white or cream markings, usually at valve junctures.

Life cycle: Chitons have separate sexes, with fertilisation occurring externally, with both eggs and sperm being released into the sea water. After fertilization, a larval trochophore develops and then metamorphoses directly into a juvenile.

Similar species: Could be confused with Tonicella marmorea or Callochiton septemvalvis.

How to see this species: It can be found on the lower shore, usually on or under boulders and the shallow sublittoral. It is most common in Strangford Lough.

Current status: Conservation status unknown.

Why is this species a priority in Northern Ireland?

• Criterion 5: Climate Change Sensitive

Threats: The major threat to this species is thought to be climate change, that is, global warming. Tonicella marmorea is a northern species at the limits of its range in Northern Ireland.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Send these to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257 or e-mail cedar.records@nationalmuseumsni.org, or via the online portal. You can also record observations including a photograph using iNaturalist, find the MBDP-NI iNaturalist project here.

Objectives:

• Perform targeted surveys to ascertain the current status of the species in Northern Ireland
• Monitor known populations to ascertain rate and extent of any potential decline.

Conservation: Most of the Northern Ireland sites lie within Strangford Lough Marine Conservation Zone (MCZ) and Marine Nature Reserve, or Rathlin Island MCZ.

Distribution Map from NBN: Boreochiton ruber at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Boreochiton ruber at iNaturalist World Species Observations database.

WoRMS: Boreochiton ruber at World Register of Marine Species. Accepted name: Boreochiton ruber (Linnaeus, 1767). AphiaID: 386411.

Classification: Biota; Animalia; Mollusca; Polyplacophora; Neoloricata; Chitonida; Acanthochitonina; Mopalioidea; Tonicellidae; Tonicellinae; Boreochiton

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(2026). Boreochiton ruber. (Linnaeus, 1767). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=W790. Accessed on 2026-07-27