Hydrozoer: Hydractinia sarsii.

The hydroid colonies of Hydractinia sarsii grow on mobile substrates, often on snail shells inhabited by hermit crabs. This species was originally described based on Norwegian specimens, but it has been recorded only a few times after that and much of its biology and ecology remains a mystery. 

Hydractinia sarsii Steenstrup, 1850
Creative Commons Attribution | Lara Beckmann | Joan J. Soto-Àngel | Aino Hosia | Luis Martell | Universitetsmuseet i Bergen, Universitetet i Bergen
Kart. Utbredelse i Norge.