- Kingdom: Animalia
- Phylum: Mollusca
- Class: Bivalvia
- Order: Myoida
- Family: Pholadidae
- Scientific name: Xylophaga dorsalis
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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?
On muddy substrate at 20 meters, in the Trondheim Fjord, Norway.
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.