(Allman, 1863)
Description
Umbrella semi-globular [Bougainvillia muscus ]; mesogloea very thick, especially in apical region; velum narrow. The four radial canals and circular canal narrow. With short and broad manubrium, sometimes slightly pedunculate. Mouth simple, circular; perradial oral tentacles inserted distinctly above mouth rim, branching dichotomously 1-2 (rarely 3-6) times, and armed with terminal nematocyst clusters.
Four interradial gonads reaching perradii, globular in females, prolonged in males [B.muscus-male].
Four small, oval marginal tentacular bulbs each with a group of 4-9 (usually 3-5) long and solid tentacles of one kind; bulbs with black, round adaxial ocelli at the base of each tentacle.
Young specimens: B.muscus-young-habitus .
Size
Umbrella 2-4 mm high and wide.
Colour
Manubrium and marginal tentacle bulbs dark reddish brown, crimson or yellowish, sometimes with greenish tinge [B.muscus-male-habitus ].
Ecology and depth range
Meropelagic; neritic. Hydroids produce medusae during spring, summer and autumn and medusae may be encountered a late as December.
Distribution in the North Sea
Throughout whole North Sea.
World distribution
North Atlantic Ocean including Mediterranean Sea; Arctic Ocean; E and W South Atlantic and Indo-Pacific Oceans.
[After Russell, 1953a; Kramp, 1959; Bouillon, 1999]