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The radioles (sense 1) of a sea urchin (subclass Euechinoidea)
The radioles (sense 2) of a feather duster worm of the genus Bispira

From Late Latin radiolus (a fossil echinoid’s spine), from Latin radius (rod, staff) (possibly ultimately from Proto-Indo-European *reh₁t- (beam, pole, post)) + -olus (diminutive suffix) (ultimately from Proto-Indo-European *-lós). The word first appears in the works of Scottish natural historian and marine zoologist Charles Wyville Thomson (1830–1882).[1]





radiole (plural radioles)

  1. (zoology) The spine of a sea urchin. [from late 19th c.]
    • 1874, Alexander Agassiz, “Terminology”, in Revision of the Echini (Illustrated Catalogue of the Museum of Comparative Zoölogy, at Harvard College; VII), part IV (Structure and Embryology of the Echini), Cambridge, Mass.: University Press; Welch, Bigelow, & Co., →OCLC, page 636:
      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.
    • 1874 April 9, [Charles] Wyville Thomson, “XXI. On the Echinoidea of the ‘Porcupine’ Deep-sea Dredging-expeditions”, in Philosophical Transactions of the Royal Society of London, volume 164, part II, London: Printed by Taylor and Francis, [], →OCLC, part I, page 725:
      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.
    • 1908, George H. Girty, “Echinoidea”, in The Guadalupian Fauna (Department of the Interior, United States Geological Survey Professional Paper; 58), Washington, D.C.: Government Printing Office, →OCLC, page 110:
      Archæocidaris sp. b. [...] This form, which is very imperfectly known, is based on two specimens. One of these shows the distal end of the radiole, which is seen to expand rather abruptly from a very slender shaft having a diameter of about three-fourths mm. into a subspherical end which has a diameter of 2 mm. The terminal portion and the shaft adjacent appear to be armed with short spinules. Associated with the foregoing is the proximal portion of a radiole, showing a long, slender, smooth, cylindrical shaft, which has a diameter of about three-fourths mm., with the usual subterminal collar near the lower end.
    • 1982 November 26, G. M. Philip, “A Pleistocene Occurrence of the Cidaroid Echinoid Genus Phyllacanthus in New Zealand”, in Robert P. Lynch, editor, New Zealand Journal of Geology and Geophysics, volume 25, number 3, Wellington: Department of Scientific and Industrial Research, →ISSN, →OCLC, page 366, column 1:
      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. (zoology) A heavily ciliated feather-like tentacle occurring in clusters on the crowns of certain tubeworms, especially those of the order Canalipalpata (the fan-head worms), used for feeding and respiration.
    • 1954, Olga Hartman, “Systematic Descriptions”, in Marine Annelids from the Northern Marshall Islands: Bikini and nearby Atolls, Marshall Islands (Geological Survey Professional Paper; 260-Q), Washington, D.C.: United States Government Printing Office, →OCLC, page 641, column 1:
      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.
    • 1990, Vernon A. Harris, “Tube-dwelling Worms (Annelida – Polychaeta)”, in Sessile Animals of the Sea Shore, London, New York, N.Y.: Chapman and Hall, →ISBN, section 7.2 (Structures Related to a Tubicolous Life Style), page 119:
      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.
    • 2011, J. D. Fish, S. Fish, “Annelida”, in A Student’s Guide to the Seashore, 3rd edition, Cambridge, Cambridgeshire: Cambridge University Press, →ISBN, pages 170–171:
      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.




  1. ^ radiole, n.”, in OED Online Paid subscription required, Oxford, Oxfordshire: Oxford University Press, June 2008; radiole”, in Lexico,; Oxford University Press, 2019–2022.

Further reading