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Hydroid stage: Each hydranth erects less than 1 cm from a creeping stolon. The stem is sometimes branched.

Medusa stage: The hemispherical or slightly flatter umbrella is less than 20 mm in diameter. There are usually four straight, radial canals, but there may be as many as 12. The gonads cover 1/3 of the radial canal length. The number of marginal tentacles are usually 32, but fewer is common on young individuals.


The medusa is a coastal plankton. The hydroids are registered from the sub-tidal zone and down to 150 meters. They grow on a wide range of substrates.


This is a cosmopolitan, known from virtually all coastal waters across the world.