This is an encrusting red algae associated with maerl beds. It is data deficient, potentially due to being inconspicuous.

In brief

• A small, encrusting red alga that is pale in colour.
• It lives in association with maerl beds and sometimes on shells.
• Data deficient, but thought to be nationally scarce.
• Due to close association with maerl beds it is subject to the same pressures.

Species description: This is small, thin, encrusting red alga. It is closely associated with maerl beds and can be inconspicuous due to its small size and pale colouration.

Life cycle: Unknown.

Similar species: Very similar to Cruoria pellita and Halarachnion ligulatum, the differences are microscopic. May require specialist identification.

How to see this species: Can be found on shells and maerl in the shallow sublittoral to 5 m.

Current status: Nationally scarce. Data deficient. Rare but thought to be relatively widely distributed around Britain and Ireland.

Why is this species a priority in Northern Ireland?

• Criterion 1: Internationally listed species.
• Criterion 3: Rare or restricted range – rare breeding species confined to 5 hectads or less (based on expert judgement).

Threats:

• Sensitive to habitat disturbance, especially bottom fishing methods or dredging.
• Close association with maerl beds so subject to same pressures as this habitat, as they would cause habitat loss or disturbance.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• The status of Cruoria cruoriiformis will be surveyed and monitored and appropriate conservation action undertaken if required.

Conservation:

• Strangford Lough is a Marine Protected Area with multiple designations.
• Rathlin Island is a Marine Protected Area with multiple designations.
• There is a Habitat Action Plan for Maerl Beds.

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

iNaturalist: Cruoria cruoriiformis at iNaturalist World Species Observations database.

WoRMS: Cruoria cruoriiformis at World Register of Marine Species. Accepted name: Cruoria cruoriiformis (P.L.Crouan & H.M.Crouan) Denizot, 1968. AphiaID: 145611.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Gigartinales; Cruoriaceae; Cruoria

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Picton, B.E., Keatley, L. & Morrow, C.C. (2026). Cruoria cruoriiformis. (P.L.Crouan & H.M.Crouan) Denizot, 1968. [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=ZM7010. Accessed on 2026-10-29