Description: The main stem of this hydroid is rather slender and the feather-like side branches are arranged in a spiral. The hydrothecae are on the upper side of the pinnae. They are grouped together in tight clusters of 2-5 hydrothecae, and there is 1 cluster to each internode. Within each cluster the hydrothecae curve alternately outwards from the axis of the pinnae. The gonothecae are oval shaped and smooth, with a short neck. The rim of the aperture is smooth.

Habitat: A typical species of tide swept, sand-scoured sites, attached to stones, boulders, wrecks and bedrock.

Distribution: A common species all round the British Isles

Similar Species: This is a very distinctive species.

Key Identification Features:

• Spiral arrangement of pinnate side branches
• Hydrothecae in clusters on finest branches

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

iNaturalist: Hydrallmania falcata at iNaturalist World Species Observations database.

WoRMS: Hydrallmania falcata at World Register of Marine Species. Accepted name: Hydrallmania falcata (Linnaeus, 1758). AphiaID: 117890.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Leptothecata; Sertularioidea; Sertulariidae; Hydrallmania