Obelia geniculata (Linnaeus, 1758)

Obelia geniculata

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:

Distribution Map from NBN: Grid map (fast) : Interactive map (slower, requires login to view records) : National Biodiversity Network mapping facility, data for UK.

 Picton, B.E. & Morrow, C.C. (2016). Obelia geniculata (Linnaeus, 1758). [In] Encyclopedia of Marine Life of Britain and Ireland. Accessed on 2017-03-27

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