- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Hydrozoa
- Subclass: Hydroidolina
- Order: Leptothecata
- Family: Campanulariidae
- Scientific name: Obelia geniculata
- Norwegian: bjellehydroide
Hydroid stage: The erect, sometimes branched stem is usually not longer than 2 cm, but in still locations stems of 5 cm have been found. The stem consists of a zigzagged arrangement of internodes of approximately regular lengths.
Medusa stage: During summer small medusae (typical diameter is 5 mm) are released in large numbers.
It is often seen growing on brown algae, Laminaria hyperborea.
Common in the Atlantic Ocean and the Indo-Pacific Oceans.