A yellow colonial sea anemone, in Northern Ireland known only from Rathlin Island. It may be vulnerable to disruption of its habitat by fishing in some locations.

In brief

• Western end of the north coast of Rathlin Island
• Grows on sponges and rocks
• Can be found throughout the year
• Listed as a priority because of its rarity in Northern Ireland
• There are few major threats to the species, but disruption of its habitat by fisheries is a possibility in some locations.

Species description: Parazoanthus axinellae is a colonial anemone forming encrustations in discreet clumps of variable thickness and shape. Individual polyps are up to 20mm in height and 5mm in diameter and are coloured a bright yellow, with orange around the mouth. The column is often encrusted with sand particles or sponge spicules (sponge skeletal structures) and its top is serrated. Between 26 and 34 pointed tentacles are arranged in two circles, the outer of these being more horizontal.

Life cycle: The sexes are separate; spawning takes place during the summer, and it is likely that planktonic larvae are produced. However, colonies are also expanded by fission, that is, partition of individuals into replicas of themselves; some workers consider this asexual method to be more important to reproduction that the sexual one.

Similar species: Parazoanthus anguicomis, has more tentacles, is generally white, and colonies tend to form more extensive sheets. P. axinellae is also larger than Isozoanthus sulcatus and Epizoanthus couchii.

How to see this species: The species is found on open coasts, at depths ranging from 6 to 100m, on rocky habitats, often attached to rocks and sponges, and often on vertical faces or beneath rocky overhangs. Four sites on Rathlin Island have been recorded, at the western end of its north coast, and elsewhere in Ireland it has been recorded in Donegal Bay, off Achill Island, Loop Head and Old Head of Kinsale, and in Britain, in Pembrokeshire and Cornwall.

Current status: In Northern Ireland, known only from Rathlin Island, four sites. The species has no legal protection.

Why is this species a priority in Northern Ireland? The species is rare and declining in Northern Ireland, and scarce throughout the UK and Ireland, and is a Species of Conservation Concern for the UK as a whole.

Threats: No particular threats are identified, but where the species occurs in more level areas of seabed, it may be vulnerable to mobile fishing gear.

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

iNaturalist: Parazoanthus axinellae at iNaturalist World Species Observations database.

WoRMS: Parazoanthus axinellae at World Register of Marine Species. Accepted name: Parazoanthus axinellae (Schmidt, 1862). AphiaID: 101055.

Classification: Biota; Animalia; Cnidaria; Anthozoa; Hexacorallia; Zoantharia; Macrocnemina; Parazoanthidae; Parazoanthus