Movie S1.

Dissection of Kuphus polythalamia. Clip 1 shows a specimen of Kuphus polythalamia, in its calcareous tube, being removed from its transport container. Clip 2 shows removal of the cap that seals the anterior end of the tube. Clip 3 shows the animal being removed from its tube. Clip 4 shows the specimen being dissected along the ventral side from the posterior to the anterior end, revealing the large gill (which appears dark brown with a black stripe along its midline, separating the left and right demibranchs) and the small visceral mass (which appears as black spherical object at the anterior end of the incision). Scale is provided by a 1-foot (30.5-cm) ruler (yellow) seen in clip 4.