Hydroids (Hydrozoa)

The species group can often be identified without enlarging aids
  • Hydroids on a Virtue disc. Photo: Mikael Olsson
  • Club-headed hydroid - close up (Photo: Anders Larsson)
  • Club-headed hydroid (Photo: Anders Larsson)
  • Halecium halecinum Sillbenshydroid. Herring-bone hydroid
  • Hydractinea echinata. Snail fur. Taggpolyp. Photo: Aquatilis

Hydroids belong to the group Cnidarians. Most hydroids live in colonies where many individuals work together. The colony consists of genetically identical individuals, called polyps. The colony is built up so that the polyps can be nourished by each other through the "stems", and various polyps may have different functions. The colonies may look different and be constructed in very different ways, which means that hydroids can be very different from each other. Therefore, it is difficult to determine the species. Hydroids can look as bright lint and can, for example, sit on shells, stones and seaweed.

More information in Aquascope

A few shallow living hydroids

Club-headed hydroid


A colony of hydroids and it´s life cycle (Article)