Spirorbis spirorbis or Spirorbis borealis is a small (3–4 mm) coiled sedentary marine polychaete worm in the Serpulidae family that lives attached to seaweeds and eel grass in shallow saltwater. It is commonly called the sinistral spiral tubeworm and is the type species of the genus Spirorbis.

S. spirorbis is a cross-fertilising hermaphrodite that broods its young in a tube attached to the worm inside the shell. The larvae are released at an advanced stage of development and spend just a few hours as free-living organisms before attaching themselves to the nearest suitable surface, often the same seaweed as the parent.

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