A radiole is a heavily ciliated feather-like

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

found in highly organized clusters on the crowns of

Canalipalpata Canalipalpata, also known as bristle-footed annelids or fan-head worms, is an order of polychaete worms, with 31 families in it including the suborder Sabellida (families Serpulidae (tubeworms) and Sabellidae (fanworms and feather duster worms) ...

. Canalipalpata is an order of

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

polychaete Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

worms consisting of 31 families (including the

Sabellidae Sabellidae, or feather duster worms, are a family of marine polychaete tube worms characterized by protruding feathery branchiae. Sabellids build tubes out of a tough, parchment-like exudate, strengthened with sand and bits of shell. Unlike the ...

Serpulidae The Serpulidae are a family (biology), family of Sessility (zoology), sessile, tube worm (body plan), tube-building annelid worms in the class Polychaeta. The members of this family differ from other Sabellidae, sabellid tube worms in that they h ...

Terebellidae The Terebellidae is a marine family of polychaete worms, of which the type taxon is '' Terebella'', described by Carl Linnaeus in his 1767 12th edition of ''Systema Naturae''. Characteristics Most terebellids live in burrows or crevices and ...

, and

Alvinellidae The Alvinellidae are a family of small, deep-sea polychaete worms endemic to hydrothermal vents in the Pacific Ocean. Belonging to the order Terebellida, the family contains two genera, ''Alvinella'' and ''Paralvinella''; the former genus cont ...

, a family of deep-sea worms associated with hydrothermal vents). These

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

tube worm A tubeworm is any worm-like sessile invertebrate that anchors its tail to an underwater surface and secretes around its body a mineral tube, into which it can withdraw its entire body. Tubeworms are found among the following taxa: * Annelida, the ...

s employ radioles primarily for

alimentation The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

. While their primary role is to function as an organ for

filter feeding Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, radioles also serve as

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

organs. Because of their role in gas exchange, radioles are often referred to as "

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s".

Anatomical location

Canalipalpata have a head located at the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end of the body. The head is formed by the fusion of a funnel-shaped, symmetrical

peristomium The peristomium is the first true body segment in an annelid worm's body in the anterior end. It is directly behind the prostomium and contains the mouth, tentacular cirri, and sometimes feeding palps, which may instead occur on the prostomium. If ...

with the

prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does not include) th ...

.Department of Biology, Walla Walla University
Serpula vermicularis
, Rosario Beach Marine Laboratory. Accessed 3 May 2010. The prostomium bears a specialized

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

which is referred to as a branchial crown. The crown functions as both a

sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. T ...

and a gill. The animal can extend the crown from its

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

tube for feeding and gas exchange, and rapidly retract it when disturbed or threatened.Richard S. Fox, Invertebrate Anatomy OnLine
''Eudistylia vancouveri''
. Lander University, 4 July 2006. Accessed 3 May 2010. 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

apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics), a teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex ...

of the funnel, between the two branchial stalks. An adult worm typically has about 40 radioles in its crown, covered by tiny, hair-like branches called

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

. This arrangement gives the crown the appearance of a small fan or feather duster (for which the animals are often referred to as

fanworm Sabellida is an order of annelid worms in the class Polychaeta. They are filter feeders with no buccal organ. The prostomium is fused with the peristomium and bears a ring of feathery feeding tentacles. They live in parchment-like tubes made of p ...

s, or

feather duster worm Sabellidae, or feather duster worms, are a family of marine polychaete tube worms characterized by protruding feathery branchiae. Sabellids build tubes out of a tough, parchment-like exudate, strengthened with sand and bits of shell. Unlike the ...

s). When extended, these heavily ciliated radioles trap particles of

organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...

and transport them towards the mouth.

Use in filter feeding

The

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

surface of each radiole is covered by cilia that rhythmically move in such a way as to create a

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

in the surrounding

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

. This current carries

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic particles from the underside of the crown upwards through the net of radioles to the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

surface. The dorsal or upper side of each radiole has a ciliated longitudinal radiolar food groove running down its center, extending along its longitudinal axis from the tip to the center of the crown. Planktonic food particles are swept into these grooves, where they become trapped in a coating of

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

. At this point, the animal subjects the particles to an examination and selection process, whereby any particles determined to be unsuitable due to size or chemical composition are rejected by the animal and discarded back into the water column. Once the selection process is complete, the cilia transport the particles towards the mouth, from where they enter the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans a ...

Use of radioles in respiration

While they are primarily feeding structures, the radioles also serve as respiratory organs.Richard S. Fox, Invertebrate Anatomy OnLine
''Serpula vermicularis''
. Lander University, 4 July 2006. Accessed 3 May 2010.An Underwater Field Guide to Point Lobos

Accessed 3 May 2010.Department of Biology, Memorial University of Newfoundland
Eudistylia_vancouveri ''Eudistylia vancouveri''
Ocean Sciences Centre. Accessed 3 May 2010. Because of this role in gas exchange, the structures are commonly referred to as "gills".

Pigmentation

The radioles of different species of Canalipalpata vary widely in color. Those of the

serpulid The Serpulidae are a family of sessile, tube-building annelid worms in the class Polychaeta. The members of this family differ from other sabellid tube worms in that they have a specialized operculum that blocks the entrance of their tubes wh ...

tubeworms are typically red, pink, or orange in color, with white transverse bands.

Astaxanthin Astaxanthin is a keto- carotenoid within a group of chemical compounds known as terpenes. Astaxanthin is a metabolite of zeaxanthin and canthaxanthin, containing both hydroxyl and ketone functional groups. It is a lipid-soluble pigment with r ...

, a

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...

pigment, is responsible for the bright red color of the crown of '' Serpula vermicularis''.

Growth and regeneration

Juvenile and other worms of small size have small crowns and radioles, so prefer to capture and eat very small particles, such as bacterioplankton and single-celled

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

and

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

. As a worm matures and grows in size, so does its crown. The larger crown allows the animal to feed on larger multicellular plankton. The preferred food size depends on the maximum size achieved by the adult worm. Canalipalpata worms often lose one or more radioles, or even the entire crown as a result of

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

by other animals or other types of trauma. Some species even appear to have the ability to control the loss of their tentacular crowns, in much the same manner as when a lizard loses its tail. In certain circumstances, sacrifice of the crown may permit escape or confer some other benefit to the animal. Separation of the crown occurs at a pre-established zone of

abscission Abscission () is the shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed. In zoology, abscission is the intentional shedding of a body part, such as the shedding of a claw, husk, or the autotomy of a ...

, located at the base of the crown. These animals have the ability to regenerate new radioles to replace those that have been

amputated Amputation is the removal of a limb by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on indivi ...

, or even the entire crown if necessary.Department of Biology, Walla Walla University
Eudistylia_vancouveri
Rosario Beach Marine Laboratory. Accessed 3 May 2010. Any would-be predators that pass by after a worm has lost its crown will get the impression that the worm has died; this protects the animal from further attack. The crown typically reappears after about two weeks. When it does reappear, it is initially smaller in size, but it eventually grows back to its former size and color.

Specialized radioles

In addition to having ordinary radioles, some Canalipalpata possess one or more highly modified radioles located on the dorsal part of the head. This specialized structure is called an '' operculum''. The operculum is a cone-shaped

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...

structure located at the distal end of a long cartilaginous stalk. When threatened or disturbed, the animal withdraws rapidly into its protective calcareous tube and employs the operculum as a plug to occlude the entrance to the tube. The operculum, which is usually similar in color to the other radioles, secretes a mucus which seems to possess

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

properties. It is not unusual for the animal to have two crowns, and hence two opercula. Serpulids and sabellids are two

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

of the

Sabellida Sabellida is an order of annelid worms in the class Polychaeta. They are filter feeders with no buccal organ. The prostomium is fused with the peristomium and bears a ring of feathery feeding tentacles. They live in parchment-like tubes made of ...

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

of Canalipalpata tubeworms that are similar in nearly every respect, but they can be readily distinguished by the fact that while both have radioles, the sabellids (such as ''

Sabella pavonina ''Sabella pavonina'', commonly known as the peacock worm, is a marine polychaete worm belonging to the family Sabellidae. They can be found along the coasts of Western Europe and the Mediterranean. It is found in shallow, tidal waters with a be ...

'') lack an operculum.

Gallery

File:Sabellastarte indica (Feather duster worm).jpg, '' Sabellastarte indica'' (Indian feather duster worm) with radioles extended File:Sabellastarte indca (Feather duster worm).jpg, ''S. indica'' with radioles extended File:Sabellastarte magnifica (Magnificent feather duster worm).jpg, ''S. magnifica'' (magnificent feather duster worm) with radioles extended File:Sabellastarte sanctijosephi (Feather duster worm) in Oceanapia amboinensis (Sponge).jpg, ''

Sabellastarte sanctijosephi ''Sabellastarte'' is a genus of marine polychaete worms in the family Sabellidae. Species The following species are classified in this genus: *''Sabellastarte assimilis'' (McIntosh, 1885) *'' Sabellastarte fallax'' (Quatrefages, 1866) *'' Sabel ...

'' (St. Joseph's feather duster worm) with radioles extended File:Sabellastarte sanctijosephi.jpg, ''S. sanctijosephi'' with radioles extended File:Sabellastarte sanctijosephi (Tubeworm).jpg, ''S. sanctijosephi'' with radioles extended File:Sabellastarte sp..jpg, ''

Sabellastarte ''Sabellastarte'' is a genus of marine polychaete worms in the Family (biology), family Sabellidae. Species The following species are classified in this genus: *''Sabellastarte assimilis'' (McIntosh, 1885) *''Sabellastarte fallax'' (Quatrefages ...

'' sp. (feather duster worm) with radioles extended File:Sabella spallanzanii.jpg, ''

Sabella spallanzanii ''Sabella spallanzanii'' is a species of marine polychaete worms in the family Sabellidae. Common names include the Mediterranean fanworm, the feather duster worm, the European fan worm and the pencil worm.Branch, G.M.; Branch, M.L.; Griffiths, ...

'' (feather duster worm) with radioles extended File:Sabella spallanzanii 2.jpg, ''S. spallanzanii'' with radioles extended File:Immagine_045.jpg, '' Spirographis'' sp. (feather duster worm) with radioles extended File:Bispira sp. (Feather duster worm).jpg, ''

Bispira ''Bispira'' is a genus of marine bristleworm Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

'' sp. (feather duster worm) with radioles extended File:Bispira sp. (Tubeworm).jpg, ''Bispira'' sp. with radioles extended Image:Sabellidae (feather duster worm) yellow.jpg,

sp. with radioles extended Image:Sabellidae (feather duster worm).jpg, Sabellidae sp. with radioles extended File:Polychaeta Sabellidae (Tubeworms) Timor.jpg, Sabellidae sp. with radioles extended File:Reef0200.jpg, Sabellidae sp. with radioles extended File:Spirobrancheus_giganteus.jpg, ''

Spirobranchus giganteus ''Spirobranchus giganteus'', commonly known as the Christmas tree worm, is a tube-building polychaete worm belonging to the family Serpulidae. Anatomy and morphology Both its common and Latin names refer to the two chromatically hued spiral s ...

'' (Christmas tree worms from East Timor)

References

{{Wiktionary Annelid anatomy Polychaetes