Christmas tree worm

Spirobranchus gigantean, or commonly known as Christmas tree worms, are tube building polychaete worms. The most distinct feature is the multi-coloured spiral, which is used to trap food and also for respiration. These creatures are sedentary, anchoring themselves in burrows that they bore into corals. When disturbed, they retract into the burrows to hide from predators. No Christmas tree worms were harmed in the making of this video, they were made to retract by simply waving a hand over them .

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What's that weird sphincter-looking thing at the left in the beginning?