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Cladonema radiatum

Cladonema radiatum

Root-arm medusa

   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)

  • Cnidaria [Phylum]
  • Hydrozoa [Class]
  • Hydroidolina [Subclass]
  • Anthoathecatae [Order]
  • Capitata [Suborder]
  • Cladonematidae [Family]
  • Cladonema radiatum Dujardin, 1843

Page glossary

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.

Cladonema radiatum. Cladonema radiatum
On Laminarian.



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 © 2006-2020.
Translation :  Anne Bay-Nouailhat © 2007-2020.

How to cite this page in publications

Bay-Nouailhat W., June 2006, Description of Cladonema radiatum, Available on line at http://www.european-marine-life.org/05/cladonema-radiatum.php, consulted on 10 July 2020.
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