Description: Obelia geniculata is readily distinguishable from other members of this genus by the structure of its stem. It forms a series of internodes that are zig-zag in their arrangement, and it is jointed at each bend. There are several annulations after each joint. Just below each joint the internodes are thickened on alternate sides, forming a 'shelf' for the support of ringed pedicels which in turn, support the hydrothecae. The hydrothecae are obconical in shape and have a smooth outer margin. The gonothecae are shaped like a grecian urn, and are also borne on ringed pedicels.

Habitat: This species normally grows on kelp fronds, especially on Laminaria hyperborea in conditions of moderate wave exposure.

Distribution: Widespread around the British Isles.

Key Identification Features:

• Zigzag, unbranched stems arising from a basal rhizome

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

iNaturalist: Obelia geniculata at iNaturalist World Species Observations database.

WoRMS: Obelia geniculata at World Register of Marine Species. Accepted name: Obelia geniculata (Linnaeus, 1758). AphiaID: 117388.

Classification: Biota; Animalia; Cnidaria; Medusozoa; Hydrozoa; Hydroidolina; Leptothecata; Campanulariidae; Obelia