Radiole

A radiole is a heavily ciliated feather-like tentacle found in highly organized clusters on the crowns of Canalipalpata. Canalipalpata is an order of sessile marine polychaete worms consisting of 31 families (including the Sabellidae, Serpulidae, Terebellidae, and Alvinellidae, a family of deep-sea worms associated with hydrothermal vents). These benthic annelid tube worms employ radioles primarily for alimentation. While their primary role is to function as an organ for filter feeding, radioles also serve as respiratory organs. Because of their role in gas exchange, radioles are often referred to as "gills".

Canalipalpata have a head located at the anterior end of the body. The head is formed by the fusion of a funnel-shaped, symmetrical peristomium with the prostomium. The prostomium bears a specialized mouth appendage which is referred to as a branchial crown. The crown functions as both a sieve and a gill. The animal can extend the crown from its calcareous tube for feeding and gas exchange, and rapidly retract it when disturbed or threatened.

The crown consists of two bundles (one right and one left) of featherlike tentacles known as branchiae, or radioles. Each of these bundles consists of a single row of radioles attached to a branchial stalk and curved into a semicircle. These two semicircles form the funnel-shaped branchial crown. The mouth is located at the of the funnel, between the two branchial stalks.

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