Hydrallmania falcata (Linnaeus, 1758)

Hydrallmania falcata

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: NBN map : National Biodiversity Network mapping facility, data for UK.

WoRMS: Species record : World Register of Marine Species.

iNaturalist: Species account : iNaturalist World Species Observations database