Schmitzia neapolitana is a small, rare, gelatinous red alga, irregularly branched and with whorls of very short branches. The whole plant is no more than 10 cm long.

In brief

• Found at only four sites in Northern Ireland: Torr Head, Loughan Bay and Cushendun Bay in County Antrim and Greenore Point in Carlingford Lough, County Down.
• Known only subtidally, to a depth of 15 m.
• Found in areas of strong currents.
• It is scarce with Northern Ireland being an Irish stronghold for this species.
• Very similar to another alga such as Calosiphonia vermicularis.
• The only threat is to its habitat.

Species description: Schmitzia neapolitana is a small, gelatinous red alga growing to more than 10 cm long. It forms a flattened leaf-like blade with opposite proliferations along the edges. The other similar species, Calosiphonia vermicularis, can only be distinguished microscopically.

Life cycle: The reproductive structures are microscopic. However reproduction and fertilization has been described in the scientific literature. The full life cycle is not known; one stage (the tetrasporophyte), if it occurs at all, has never been recorded in Northern Ireland.

Similar species: Schmitzia neapolitana is very similar to Calosiphonia vermicularis; microscopic examination is required to distinguish them.

How to see this species: In Northern Ireland this species has only been recorded from Torr Head, Loughan Bay and Cushendum Bay in County Antrim. The only record from County Down is from Greenore Point in Carlingford Lough. It grows below low-water mark to 15 m depth on small stones and boulders in places of strong currents. It is best searched for by SCUBA diving.

Current status: Rare, data deficient. It has only been recorded from four sites in Northern Ireland: Torr Head, Loughan Bay and Cushendun Bay in County Antrim, and Greenore Point in Carlingford Lough, County Down. All Irish records are from Northern Ireland.

Why is this species a priority in Northern Ireland?

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

Threats:

• The only known threat is to its habitat.
• It may also be sensitive to changes in water quality.

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 Schmitzia neapolitana will be surveyed and monitored and appropriate conservation action undertaken if required.

Conservation:

• Rathlin Island is a Marine Protected Area with multiple designations.
• Implementation of the Northern Ireland Habitat Action Plan for Maerl Beds.

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

iNaturalist: Schmitzia neapolitana at iNaturalist World Species Observations database.

WoRMS: Schmitzia neapolitana at World Register of Marine Species. Accepted name: Schmitzia neapolitana (Berthold) P.C.Silva, 1959. AphiaID: 145604.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Gigartinales; Calosiphoniaceae; Schmitzia

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Adapted from text by Osborne Morton (2026). Schmitzia neapolitana. (Berthold) Lagerheim ex P Silva. [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=ZM5600. Accessed on 2026-09-13