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The Christmas tree worm, Spirobranchus giganteus. This sedentarian’s two tree-shaped whorls are tentacles, which it uses in gas exchange and to collect food particles from the water. The tentacles emerge from a calcium carbonate tube secreted by the worm that protects and supports its soft body.
Source: Urry, Lisa A.. Campbell Biology (p. 701). Pearson Education. Kindle Edition.

Sedentaria (Campbell Biology)

Species in the other major clade of annelids, Sedentaria (from the Latin sedere, sit), tend to be less mobile than those in Errantia. Some species burrow slowly through marine sediments or soil, while others live within tubes that protect and support their soft bodies. Tube-dwelling sedentarians often have elaborate gills or tentacles used for filter feeding. Although the Christmas tree worm shown in the photo above once was classified as a “polychaete,” current evidence indicates it is a sedentarian. The clade Sedentaria also contains former “oligochaetes.”


Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition.


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