radiole

noun

1. The spine of a sea urchin.

   “Radioles or spines [...] are the appendages articulating upon the tubercles. The different parts of the spines are the socket by which it is articulated to the tubercles; the lower part of the radiole is called the head, and is separated from the neck, which is usually smooth or finely striated, by the milled ring,—a prominent ridge more or less deeply grooved, serving as an attachment for the muscles which are to move the spine; beyond the neck we have the body or shaft of the spine.”

   “The radioles of the second size are about 8 millims. in length and 2 millims. in width, very much compressed and flattened, rounded at the end and finely striated longitudinally. They are articulated in a single row to the small tubercles round the edge of the areola, and in their natural attitude they lean over the naked part of the areola and cover the muscles and the head of the large radiole like a frill.”

   “The species P. wellmanae would here be synonymised with P. duncani if only the holotype test was known. The younger Te Piki test fragments are indistinguishable from P. wellmanae (and P. duncani), but the radioles differ from those of P. duncani (i.e., P. wellmanae is here being distinguished by features not seen in this holotype). Discovery of topotype radioles will be necessary to confirm the present interpretation and usage.”

2. A heavily ciliated feather-like tentacle occurring in clusters on the crowns of certain tubeworms, especially those of the order Canalipalpata (fan-head worms), used for feeding and respiration.

   “Fabricia bikinii, n. sp. [...] The tentacular crown is composed of three pairs of symmetrical radioles; in addition there are shorter, entire, paired filamentous processes, or palpi, at the ventral end of the crown [...]. Each radiole has 6 to 8 pairs of slender filaments that arise along the basal half of the radiole; these filaments extend distally not quite as far as the radioles to which they are attached.”

   “The anterior segments of sabellid and serpulid worms are modified in two important ways: the head has a crown of pinnate radioles arranged in two spirals or semicircles above the mouth, and some of the anterior segments form a thoracic region [...]. In the Serpulidae, one (sometimes two) of the radioles is modifed as an operculum, which blocks the mouth of the tube when the worm retreats.”

   “Family Sabellidae [...] Head with a characteristic crown of 2 groups of pinnate projections called radioles [...], which sometimes bear eyes, and project from the tube when the worm is feeding.”