Cladonema radiatum is a small anthomedusa whose dome-shaped umbrella reached
6 mm in diameter. The whitish manubrium which bears the gonads can be seen through the translucent umbrella.
On the margin of the umbrella, there are generally eight elongated bulbs from where branched tentacules stretch out.
Under each one of these bulbs, 1 to 4 stalked buttons are used to stick on the substratum. The root-arm medusa
often settles on seaweeds and Zostera. Belonging to planktonic species, it has a hopping way of swimming, then
it suddenly folds its tentacles and let itself fall. Present from June to October, it can be very abundant
during warm periods and can cause tingling sensation to bathers. This little medusa is the sexual swimming form
of a small hydroid living fixed to seaweeds, marine plants and rocks.
It is found in the North-Atlantic Ocean, the North Sea, the English Channel and the Mediterranean Sea. It is also listed in Japan.
(source : European Register of Marine Species)
Anthomedusa : Medusa elonging to the order Anthoathecatae. During their life cycle, they alternate a
sessile polyp generation with a swimming medusa one.
Umbrella : External layer of the medusa generally bell-shaped.
Manubrium : Tubular gastric cavity ended by the mouth.
Gonad : Pouch containing sexual cells.
Substratum : Surface where an organism lives in or on.
Plankton : Free swimming animal or vegetal living in sea or fresh water.
Top photograph :
© Wilfried Bay-Nouailhat. Published with author's kind permission :
Cladonema radiatum, In laboratory.
Bottom photograph : © Wilfried Bay-Nouailhat. Published with author's kind permission :
Cladonema radiatum, On Laminarian.. Bay of Concarneau, South-Brittany, West of France. Depth 5 meters.
Text : Wilfried Bay-Nouailhat © 2006-2014.
Translation : Anne Bay-Nouailhat © 2007-2014.