• Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Bivalvia
  • Order: Myoida
  • Family: Pholadidae
  • Scientific name: Xylophaga dorsalis

Description:

It looks like eggs of some kind. The height of the cylinders are 3-5 cm. Inside some of them there seems to be a tiny creature, perhaps the mother?

Habitat:

On muddy substrate at 20 meters, in the Trondheim Fjord, Norway.

Solved:

Thanks, again to Erling Svensen for solving this one, too. These are piddocks, probably Xylophaga dorsalis. The white, cylindrical columns are faeces. A siphon can be seen inside some of the cylinders.