- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Hydrozoa
- Subclass: Hydroidolina
- Order: Anthoathecata
- Suborder: Filifera
- Family: Hydractiniidae
- Scientific name: Hydractinia echinata
- Norwegian: eremittkrepshydroide
Hydroid stage: The snail fur forms a 3 mm horny mat with 1-2 mm spines. The polyps may grow to a height of 13 mm. There are four types of polyps:
- The club shaped hydranths have two circles of tentacles, with eight tentacles in each.
- Female and male gonozooids are shorter and have fewer tentacles. The gonozooids spawn planula (free-swimming) larvae. These detect detect moving shells and attach themselves to them.
- The dactylozooids are long threadlike individuals.
Medusa stage: No information.
This hydroid is well known along the European coasts, from the Mediterranean to the Arctic.