Description: Halecium halecinum is the commonest Halecium species. The colonies are variable in shape but basically consist of a strong, straight main stem, with strong secondary straight branches and tertiary branches bearing polyps. These branch at approximately 50 degrees to, and in the same plane as the stem from which they arise. The polyps are only partially retractile into cylindrical thecae which have out-turned rims. Colonies typically 50-100mm in height.

Habitat: A common and often abundant species in the infralittoral and ciralittoral zones. It is most frequently found on horizontal or inclined rock surfaces in slight to moderate tidal streams. It is generally absent from areas with stong currents but may occur in sheltered microhabitats.

Ecology: The nudibranchs Doto fragilis, Cuthona amoena and Cuthona rubescens may all be found feeding on this hydroid.

Distribution: Found all around the coasts of the British Isles.

Similar Species: Other Halecium species have similarly shaped thecae and fine branching, but the overall colony shape of Halecium halecinum is distinctive. The most similar species is Halecium beanii.

Key Identification Features:

• Regular branching with straight main stems and alternate side branches in two dimensional colony.
• Hydrothecae are goblet-shaped with rims slightly turned out.
• Gonothecae are smooth and ovate in shape.

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

iNaturalist: Halecium halecinum at iNaturalist World Species Observations database.

WoRMS: Halecium halecinum at World Register of Marine Species. Accepted name: Halecium halecinum (Linnaeus, 1758). AphiaID: 231751.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Leptothecata; Haleciidae; Halecium