Hydroids are quite easy to obtain from medusa but they are very small, maximum 0.6 mm high. It makes it almost impossible to find them in nature. On September 13th 2002 I found five reduced hydroids on translucent plastic floating in the marina in Zeebrugge. Medusa are present in Zeebrugge from half May until the end of October, sometimes in large quantities. The medusa typically have a pair of club-shaped tentacles in the middle of each tentacle bulbus. It was observed how the club-shaped tentacles developed from normal tentacles. A medusa of 2.5 mm was sampled, it had 4 long tentacles on each bulbus. The next day, the 2 middlemost tentacles contracted to form the club-shaped tentacles. A medusa of 3-4 mm has 6 tentacles, the middlemost already club-shaped, but still able to extend them for a reasonable length. Statistics of measurements in relation to the number of tentacles and branching of the stomach tentacles are made on 120 individuals.
