Polychaeta () is a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; : parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed late ...

that bear many bristles, called

chaeta A chaeta or cheta (; ) is a chitinous bristle or seta found on annelid worms, although the term is also frequently used to describe similar structures in other invertebrates such as arthropods. Polychaete annelids (''polychaeta'' literally me ...

e, which are made of

chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...

. More than 10,000 species are described in this class. Common representatives include the

lugworm ''Arenicola'', also known as sandworms, is a genus of capitellid annelid worms comprising the lugworms and black lugs. ''A.cristata'' is the dominant warm-water lugworm on the shores of North America and Humboldt Bay, California. ''A. caroledna' ...

(''Arenicola marina'') and the sandworm or clam worm ''Alitta''. Polychaetes as a class are robust and widespread, with species that live in the coldest ocean temperatures of the

abyssal plain An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They ...

, to forms which tolerate the extremely high temperatures near

hydrothermal vent Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hot ...

s. Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

near the surface, to a 2- to 3-cm specimen (still unclassified) observed by the robot ocean probe ''Nereus'' at the bottom of the

Challenger Deep The Challenger Deep is the List of submarine topographical features#List of oceanic trenches, deepest known point of the seabed of Earth, located in the western Pacific Ocean at the southern end of the Mariana Trench, in the ocean territory o ...

, the deepest known spot in the Earth's oceans. Only 168 species (less than 2% of all polychaetes) are known from fresh waters.

Description

Polychaetes are segmented worms, generally less than in length, although ranging at the extremes from to , in ''

Eunice aphroditois ''Eunice aphroditois'' is a Benthic zone, benthic polychaete, bristle worm of warm marine waters. It lives mainly in the Atlantic Ocean, but can also be found in the Indo-Pacific. It ranges in length from less than to nearly . Its exoskeleton d ...

''. They can sometimes be brightly coloured, and may be

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstruc ...

or even

luminescent Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an objec ...

. Each segment bears a pair of paddle-like and highly vascularized

, which are used for movement and, in many species, act as the worm's primary

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 gr ...

surfaces. Bundles of bristles, called

e, project from the parapodia. However, polychaetes vary widely from this generalized pattern, and can display a range of different body forms. The most generalised polychaetes are those that crawl along the bottom, but others have adapted to many different

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

s, including burrowing, swimming,

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

life, tube-dwelling or boring,

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

ism, and

parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

, requiring various modifications to their body structures. The head, or

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

, is relatively well developed, compared with other annelids. It projects forward over the mouth, which therefore lies on the animal's underside. The head normally includes two to four pair of eyes, although some species are blind. These are typically fairly simple structures, capable of distinguishing only light and dark, although some species have large eyes with lenses that may be capable of more sophisticated vision, including the Alciopids' complex eyes which rival cephalopod and vertebrate eyes. Many species show

bioluminescence Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...

; eight families have luminous species. The head also includes a pair of antennae, tentacle-like

palp Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicera ...

s, and a pair of pits lined with

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

, known as "nuchal organs". These latter appear to be

chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorece ...

s, and help the worm to seek out food.

Internal anatomy and physiology

The outer surface of the body wall consists of a simple

columnar epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of many ...

covered by a thin

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

. Underneath this, in order, are a thin layer of connective tissue, a layer of circular muscle, a layer of longitudinal muscle, and a

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesotheli ...

surrounding the

body cavity A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, a ...

. Additional oblique muscles move the parapodia. In most species the body cavity is divided into separate compartments by sheets of peritoneum between each segment, but in some species it is more continuous. The mouth of polychaetes is located on the

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 ...

, the segment behind the

, and varies in form depending on their diets, since the group includes predators, herbivores, filter feeders, scavengers, and parasites. In general, however, they possess a pair of jaws and a

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

that can be rapidly everted, allowing the worms to grab food and pull it into their mouths. In some species, the pharynx is modified into a lengthy

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

. The digestive tract is a simple tube, usually with a stomach part way along. The smallest species, and those adapted to burrowing, lack

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, 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 r ...

s, breathing only through their body surfaces. Most other species have external gills, often associated with the parapodia. A simple but well-developed circulatory system is usually present. The two main blood vessels furnish smaller vessels to supply the parapodia and the gut. Blood flows forward in the dorsal vessel, above the gut, and returns down the body in the ventral vessel, beneath the gut. The blood vessels themselves are contractile, helping to push the blood along, so most species have no need of a heart. In a few cases, however, muscular pumps analogous to a heart are found in various parts of the system. Conversely, some species have little or no circulatory system at all, transporting oxygen in the coelomic fluid that fills their body cavities. The blood may be colourless, or have any of three different respiratory pigments. The most common of these is

haemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobi ...

, but some groups have haemerythrin or the green-coloured chlorocruorin, instead. The nervous system consists of a single or double ventral nerve cord running the length of the body, with

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

and a series of small nerves in each segment. The brain is relatively large, compared with that of other annelids, and lies in the upper part of the head. An

endocrine gland The endocrine system is a network of glands and organs located throughout the body. Along with the nervous system, it makes the neuroendocrine system, which controls and regulates many of the body's functions. Endocrine glands are ductless gland ...

is attached to the ventral posterior surface of the brain, and appears to be involved in reproductive activity. In addition to the sensory organs on the head, photosensitive eye spots,

statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, crustaceans, and gastropods, A similar structure is also found in '' Xenoturbella''. T ...

s, and numerous additional sensory nerve endings, most likely involved with the sense of touch, also occur on the body. Polychaetes have a varying number of protonephridia or

metanephridia The nephridium (: nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Nephridia co ...

for excreting waste, which in some cases can be relatively complex in structure. The body also contains greenish " chloragogen" tissue, similar to that found in

oligochaete Oligochaeta () is a subclass of soft-bodied animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadril ...

s, which appears to function in metabolism, in a similar fashion to that of the vertebrate

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

. The cuticle is constructed from cross-linked fibres of

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

and may be 200 nm to 13 mm thick. Their jaws are formed from sclerotised collagen, and their

setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

from sclerotised

Ecology

Polychaetes are predominantly marine, but many species also live in freshwater, and a few in terrestrial environments. They are extremely variable in both form and lifestyle, and include a few taxa that swim among the

or above the

. Most burrow or build tubes in the sediment, and some live as

s. A few species, roughly 80 (less than 0.5% of species), are parasitic. These include both

ectoparasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...

and

endoparasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

. Ectoparasitic polychaetes feed on skin, blood, and other secretions, and some are adapted to bore through hard, usually calcerous surfaces, such as the shells of mollusks. These "boring" polychaetes may be parasitic, but may be opportunistic or even obligate symbionts (commensals). The mobile forms (

Errantia Errantia is a diverse group of marine life, marine polychaete worms in the phylum Annelida. Traditionally a subclass (biology), subclass of the paraphyletic class Polychaeta, it is currently regarded as a monophyletic group within the larger Pleis ...

) tend to have well-developed sense organs and jaws, while the stationary forms (

Sedentaria Sedentaria is a diverse clade of annelid worms. It is traditionally treated as a subclass of the paraphyletic class Polychaeta, but it is also a monophyletic group uniting several polychaetes and the monophyletic class Clitellata. It is the sis ...

) lack them, but may have specialized gills or tentacles used for respiration and deposit or filter feeding, e.g.,

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 ...

s. Underwater polychaetes have eversible mouthparts used to capture prey. A few groups have evolved to live in terrestrial environments, like Namanereidinae with many terrestrial species, but are restricted to humid areas. Some have even evolved cutaneous invaginations for aerial gas exchange.

Notable polychaetes

*One notable polychaete, the Pompeii worm (''Alvinella pompejana''), is endemic to the

s of the Pacific Ocean. Pompeii worms are among the most heat-tolerant complex animals known. *A recently discovered genus, ''

Osedax ''Osedax'' is a genus of deep-sea siboglinid polychaetes, commonly called boneworms, zombie worms, or bone-eating worms. ''Osedax'' is Latin for "bone-eater". The name alludes to how the worms bore into the bones of whale carcasses to reach en ...

'', includes a species nicknamed the " bone-eating snot flower". *Another remarkable polychaete is '' Hesiocaeca methanicola'', which lives on

methane clathrate Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large a ...

deposits. *'' Lamellibrachia luymesi'' is a

cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where seepage of fluids rich in hydrogen sulfide, methane, and other hydrocarbons occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature ...

tube worm that reaches lengths of over 3 m and may be the most long-lived annelid, being over 250 years old. *A still unclassified multilegged predatory polychaete worm was identified only by observation from the underwater vehicle ''Nereus'' at the bottom of the

, the greatest depth in the oceans, near in depth. It was about an inch long visually, but the probe failed to capture it, so it could not be studied in detail. *The Bobbit worm (''

'') is a predatory species that can achieve a length of ), with an average diameter of . *''Dimorphilus gyrociliatus'' has the smallest known genome of any annelid. The species shows extreme

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. Females measure ~1 mm long and have simplified bodies containing six segments, a reduced coelom, and no appendages, parapodia, or chaetae. The males are only 50 μm long and consist of just a few hundred cells. They lack a digestive system and have just 68 neurons, and only live for roughly a week.

Reproduction

Most polychaetes have separate sexes, rather than being hermaphroditic. The most primitive species have a pair of

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s in every segment, but most species exhibit some degree of specialisation. The gonads shed immature

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s directly into the body cavity, where they complete their development. Once mature, the gametes are shed into the surrounding water through ducts or openings that vary between species, or in some cases by the complete rupture of the body wall (and subsequent death of the adult). A few species

copulate Sexual intercourse (also coitus or copulation) is a sexual activity typically involving the insertion of the erect male penis inside the female vagina and followed by thrusting motions for sexual pleasure, reproduction, or both.Sexual inte ...

, but most fertilize their eggs externally. The fertilized eggs typically hatch into

trochophore A trochophore () is a type of free-swimming planktonic marine larva with several bands of cilia. By moving their cilia rapidly, they make a water eddy to control their movement, and to bring their food closer in order to capture it more easily. ...

larvae, which float among the

, and eventually

metamorphose Metamorphosis is a biological process by which an animal physically developmental biology, develops including birth, birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through ...

into the adult form by adding segments. A few species have no larval form, with the egg hatching into a form resembling the adult, and in many that do have larvae, the trochophore never feeds, surviving off the yolk that remains from the egg. However, some polychaetes exhibit remarkable reproductive strategies. Some species reproduce by epitoky. For much of the year, these worms look like any other burrow-dwelling polychaete, but as the breeding season approaches, the worm undergoes a remarkable transformation as new, specialized segments begin to grow from its rear end until the worm can be clearly divided into two halves. The front half, the atoke, is asexual. The new rear half, responsible for breeding, is known as the epitoke. Each of the epitoke segments is packed with eggs and sperm and features a single eyespot on its surface. The beginning of the last lunar quarter is the cue for these animals to breed, and the epitokes break free from the atokes and float to the surface. The eye spots sense when the epitoke reaches the surface and the segments from millions of worms burst, releasing their eggs and sperm into the water. A similar strategy is employed by the deep sea worm '' Syllis ramosa'', which lives inside a

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

. The rear ends of the worm develop into "stolons" containing the eggs or sperm; these stolons then become detached from the parent worm and rise to the sea surface, where fertilisation takes place.

Fossil record

Stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

polychaete fossils are known from the

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...

Lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

, a rich, sedimentary deposit in Greenland tentatively dated to the late

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxi ...

(early

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

). The oldest found is '' Phragmochaeta canicularis''. Many of the more famous

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

organisms, such as '' Canadia'', may also have polychaete affinities. ''

Wiwaxia ''Wiwaxia'' is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. ''Wiwaxia'' fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early C ...

'', long interpreted as an annelid, is now considered to represent a mollusc. An even older fossil, '' Cloudina'', dates to the terminal

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

period; this has been interpreted as an early polychaete, although consensus is absent. Being soft-bodied organisms, the fossil record of polychaetes is dominated by their fossilized jaws, known as

scolecodont A scolecodont is the jaw of a polychaete annelid, a common type of fossil-producing segmented worm useful in invertebrate paleontology. Scolecodonts are common and diverse microfossils, which range from the Cambrian period (around half a billion ...

s, and the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

ized tubes that some of them secrete. Most important

biomineralising polychaetes Biomineralising polychaetes are polychaetes that produce minerals to harden or stiffen their own tissues (biomineralize). The most important biomineralizing polychaetes are serpulids, sabellids and cirratulids. They secrete tubes of calcium ...

are serpulids, sabellids, and cirratulids. Polychaete cuticle does have some

preservation potential Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov ...

; it tends to survive for at least 30 days after a polychaete's death. Although biomineralisation is usually necessary to preserve soft tissue after this time, the presence of polychaete muscle in the nonmineralised Burgess shale shows this need not always be the case. Their preservation potential is similar to that of

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

Taxonomy and systematics

Taxonomically, polychaetes are thought to be

, meaning the group excludes some descendants of its most recent common ancestor. Groups that may be descended from the polychaetes include the

clitellate The Clitellata are a class of annelid worms, characterized by having a clitellum – the 'collar' that forms a reproductive cocoon during part of their life cycles. The clitellates comprise around 8,000 species. Unlike the class of Polychaeta, ...

s (

earthworm An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass, depending on the author) Oligochaeta. In classical systems, they we ...

s and

leech Leeches are segmented parasitism, parasitic or Predation, predatory worms that comprise the Class (biology), subclass Hirudinea within the phylum Annelida. They are closely related to the Oligochaeta, oligochaetes, which include the earthwor ...

es),

sipuncula The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of marine annelid worms, that have secondarily lost their segmentation. Sipuncula was once considered a phylum of unsegmented ...

ns, and

echiura The Echiura, or spoon worms, are a small group of ocean, marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into Segmentation (biology), segments, but e ...

ns. The Pogonophora and Vestimentifera were once considered separate phyla, but are now classified in the polychaete family

Siboglinidae Siboglinidae is a family (biology), family of polychaete Annelida, annelid worms whose members made up the former phylum, phyla Pogonophora and Vestimentifera (the giant tube worms). The family is composed of around 100 species of vermiform creatu ...

. Much of the classification below matches Rouse & Fauchald, 1998, although that paper does not apply ranks above family. Older classifications recognize many more (sub)orders than the layout presented here. As comparatively few polychaete

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

have been subject to

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

analysis, some groups which are usually considered invalid today may eventually be reinstated. These divisions were shown to be mostly paraphyletic in recent years. * Basal or ''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' **Family Diurodrilidae **Family Histriobdellidae **Family Nerillidae **Family Parergodrilidae **Family Potamodrilidae **Family Psammodrilidae **Family

Spintheridae Spintheridae is a family of marine polychaete worms with a single genus, ''Spinther'', containing these species: * '' Spinther alaskensis'' Hartman, 1948 * '' Spinther arcticus'' (M. Sars, 1851) (includes '' Spinther miniaceus'' Grube, 1860) *'' ...

**Family Protodriloididae **Family Saccocirridae **Order Haplodrili **Order

Myzostomida The Myzostomida or Myzostomatida are an order of small marine (ocean), marine worms, which are Parasitism, parasitic on echinoderms, mostly crinoids. These highly unusual and diverse annelids were first discovered by Friedrich Sigismund Leuckart ...

***Family Endomyzostomatidae ***Family Asteromyzostomatidae ***Family

Myzostomatidae Myzostomatidae is a family of polychaetes belonging to the order Myzostomida The Myzostomida or Myzostomatida are an order of small marine (ocean), marine worms, which are Parasitism, parasitic on echinoderms, mostly crinoids. These highly un ...

*Subclass Palpata **Family

Protodrilidae Protodrilidae is a family of polychaetes belonging to the order Protodrilida. Genera: * ''Astomus'' Jouin, 1979 * ''Claudrilus'' Martínez, Di Domenico, Rouse & Worsaae, 2015 * ''Lindrilus'' Martínez, Di Domenico, Rouse & Worsaae, 2015 * ''Mega ...

**Family Polygordiidae *Subclass

Aciculata Errantia is a diverse group of marine life, marine polychaete worms in the phylum Annelida. Traditionally a subclass (biology), subclass of the paraphyletic class Polychaeta, it is currently regarded as a monophyletic group within the larger Pleis ...

**Family Levidoridae **Order

Amphinomida Amphinomida is an order of marine polychaetes. The order contains two families: * ''Amphinomidae Amphinomidae, also known as the fireworms, bristle worms or sea mice, are a family (biology), family of marine polychaetes, many species of which ...

***Family

Amphinomidae Amphinomidae, also known as the fireworms, bristle worms or sea mice, are a family (biology), family of marine polychaetes, many species of which bear chaetae mineralized with carbonate. The best-known amphinomids are the fireworms, which can ca ...

***Family

Euphrosinidae The Euphrosinidae are a family of polychaete worms. The name is from Greek ''Euphrosyne'', meaning merriment; she was one of the three Graces. Clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is ...

**Order

Eunicida Eunicida is an order of polychaete worms. Characteristics Members of this order have an elongated, segmented body and a distinct head, normally with a separate peristomium and prostomium. Many, but not all, live in tubes which vary from a mucou ...

***Family Dorvilleidae ***Family

Eunicidae Eunicidae is a family of marine polychaetes (bristle worms). The family comprises marine annelids distributed in diverse benthic habitats across Oceania, Europe, South America, North America, Asia and Africa. The Eunicid anatomy typically consi ...

***Family Hartmaniellidae ***Family Ichthyotomidae ***Family Lumbrineridae ***Family Oenonidae ***Family Onuphidae **Order

Phyllodocida Phyllodocida is an order of polychaete worms in the subclass Aciculata. These worms are mostly marine, though some are found in brackish water. Most are active benthic creatures, moving over the surface or burrowing in sediments, or living in cr ...

***Suborder Aphroditiformia ****Family

Acoetidae Acoetidae is a family of polychaete worms in the order Phyllodocida. Genera * '' Acoetes'' Audouin & Milne Edwards, 1832 * '' Euarche'' Ehlers, 1887 * '' Eupanthalis'' McIntosh, 1876 * '' Eupolyodontes'' Buchanan, 1894 * '' Neopanthalis'' Stre ...

****Family

Aphroditidae Aphroditidae is a family of annelids belonging to the order Phyllodocida. Genera Genera: * '' Aphrodita'' Linnaeus, 1758 * '' Aphrogenia'' Kinberg, 1856 * '' Cyanippa'' Lucas, 1840 * '' Halogenia'' Horst, 1916 * '' Hermione'' Blainville,1828 * ' ...

****Family

Eulepethidae Eulepethidae is a family of polychaetes belonging to the order Phyllodocida Phyllodocida is an order of polychaete worms in the subclass Aciculata. These worms are mostly marine, though some are found in brackish water. Most are active benthi ...

****Family Iphionidae ****Family

Pholoidae Pholoidae is a family of polychaetes belonging to the order Phyllodocida Phyllodocida is an order of polychaete worms in the subclass Aciculata. These worms are mostly marine, though some are found in brackish water. Most are active benthic c ...

****Family

Polynoidae Polynoidae is a family (biology), family of marine Polychaete worms known as "scale worms" due to the scale-like elytron (Annelida), elytra on the dorsal surface. Almost 900 species are currently recognised belonging to 9 subfamilies and 167 gen ...

****Family Sigalionidae ***Suborder Glyceriformia ****Family Glyceridae ****Family Goniadidae ****Family Lacydoniidae ****Family Paralacydoniidae ***Suborder Nereidiformia ****Family Antonbruunidae ****Family Chrysopetalidae ****Family

Hesionidae Hesionidae are a family of phyllodocid bristle worms (class Polychaeta). They are (like almost all polychaetes) marine organisms. Most are found on the continental shelf; '' Hesiocaeca methanicola'' is found on methane ice, where it feeds on ...

****Family Nereididae ****Family Pilargidae ****Family Syllidae ***Suborder Phyllodocida incertae sedis ****Family Iospilidae ****Family Nautiliniellidae ****Family Nephtyidae ****Family Typhloscolecidae ****Family Tomopteridae ***Suborder Phyllodociformia ****Family Alciopidae ****Family Lopadorrhynchidae ****Family

Phyllodocidae Phyllodocidae is a Family (biology), family of polychaete worms. Worms in this family live on the seabed and may burrow under the sediment. Characteristics Members of the Phyllodocidae are characterised by an eversible pharynx and leaf-like dors ...

****Family Pontodoridae *Subclass

**Family

Chaetopteridae The Chaetopteridae are a Family (biology), family of marine filter feeding, filter-feeding Polychaete, polychaete worms that live in vertical or U-shaped tubes in tunnels buried in the sedimentary or hard substrate of marine environments. The wo ...

**Infraclass

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 worm ...

***Order

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 o ...

****Family Caobangidae ****Family Fabriciidae ****Family Oweniidae ****Family Sabellariidae ****Family

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 th ...

****Family

Serpulidae 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 w ...

****Family

(formerly the phyla Pogonophora & Vestimentifera) ***Order

Spionida Spionida is an order (biology), order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the Littoral zone, littoral or neritic zones. Characteristics Spionids have a single pair ...

****Suborder Spioniformia *****Family

Apistobranchidae Apistobranchidae is a family of polychaetes belonging to the order Spionida Spionida is an order (biology), order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the Littoral ...

*****Family

Longosomatidae Longosomatidae is a family of polychaetes belonging to the order Spionida Spionida is an order (biology), order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the Littoral z ...

*****Family

Magelonidae Magelonidae is a family of annelids belonging to the order Spionida. Genera: * '' Dannychaeta'' Chen, Parry, Vinther, Zhai, Hou & Ma, 2020 * '' Magelona'' Müller, 1858 * '' Meridithia'' Hernández-Alcántara & Solís-Weiss, 2000 * '' Octomage ...

*****Family

Poecilochaetidae Poecilochaetidae is a family of marine worms within the Polychaeta. It is a monotypic family containing the single genus '' Poecilochaetus''. Members of this family are benthic The benthic zone is the ecological region at the lowest level of ...

*****Family

Spionidae Spionidae is a family of marine worms within the Polychaeta. Spionids are selective deposit feeders that use their two grooved palps to locate prey. However, some spionids are capable of interface feeding, i.e. switching between deposit and sus ...

*****Family

Trochochaetidae Trochochaetidae is a family of polychaetes belonging to the order Spionida Spionida is an order (biology), order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the Littoral ...

*****Family

Uncispionidae Uncispionidae is a family of polychaetes belonging to the order Spionida Spionida is an order (biology), order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the Littoral zo ...

***Order

Terebellida Terebellida make up an Order (biology), order of the Polychaete, Polychaeta class (biology), class, commonly referred to as "bristle worms". Together with the Sabellida, the Spionida and Incertae sedis, some enigmatic families of unclear Taxonomy ...

****Suborder Cirratuliformia *****Family Acrocirridae (sometimes placed in Spionida) *****Family

Cirratulidae Cirratulidae is a family of marine polychaete worms. Members of the family are found worldwide, mostly living in mud or rock crevices. Most are deposit feeders, but some graze on algae or are suspension feeders. Although subject to multiple re ...

(sometimes placed in Spionida) *****Family Ctenodrilidae (sometimes own suborder Ctenodrilida) *****Family Fauveliopsidae (sometimes own suborder Fauveliopsida) *****Family Flabelligeridae (sometimes suborder Flabelligerida) *****Family Flotidae (sometimes included in Flabelligeridae) *****Family Poeobiidae (sometimes own suborder Poeobiida or included in Flabelligerida) *****Family Sternaspidae (sometimes own suborder Sternaspida) ****Suborder Terebellomorpha *****Family Alvinellidae *****Family Ampharetidae *****Family Pectinariidae *****Family Terebellidae *****Family Trichobranchidae **Infraclass

Scolecida Scolecida is an Infraclass (biology), infraclass of polychaete worms. Scolecids are mostly unselective Detritivore, deposit feeders on marine detritus. Characteristics Scolecids have Parapodium, parapodia with rami that are all alike. The pros ...

***Family

Arenicolidae Arenicolidae is a family of marine polychaete worms. They are commonly known as lugworms and the little coils of sand they produce are commonly seen on the beach. Arenicolids are found worldwide, mostly living in burrows in sandy substrates. Most ...

***Family

Capitellidae Capitellidae is a polychaete worm family in the subclass Scolecida Scolecida is an Infraclass (biology), infraclass of polychaete worms. Scolecids are mostly unselective Detritivore, deposit feeders on marine detritus. Characteristics Scolec ...

***Family Cossuridae ***Family

Maldanidae Maldanidae is a family of more than 200 species of marine polychaetes commonly known as bamboo worms or maldanid worms. They belong to the order Capitellida, in the phylum Annelida. They are most closely related to family Arenicolidae, and toget ...

***Family Opheliidae ***Family

Orbiniidae Orbiniidae is a family of polychaete worms. Orbiniids are mostly unselective deposit feeders on marine detritus. They can be found from the neritic zone to abyssal depths. The family was revised in 1957 by Olga Hartman and some further revisi ...

***Family Paraonidae ***Family Scalibregmatidae ***Order

Capitellida Capitellida is an order of marine sedentarian annelids The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, a ...

(

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

) ***Order Cossurida (nomen dubium) ***Order Opheliida (nomen dubium) ***Order

Orbiniida Orbiniida is an order of small polychaete worms in the phylum Annelida. It is the earliest diverging clade in Sedentaria. Along with Protodriliformia (in Errantia), this order is composed of meiofaunal marine worms formerly known as " archiann ...

(nomen dubium) ***Order Questida (nomen dubium) ***Order Scolecidaformia (nomen dubium) *Subclass

Echiura The Echiura, or spoon worms, are a small group of ocean, marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into Segmentation (biology), segments, but e ...

** Order Bonelliida *** Family Bonelliidae *** Family Ikedidae ** Order Echiurida *** Family Echiuridae *** Family Thalassematidae *** Family Urechidae

References

Bibliography

* Campbell, Reece, and Mitchell. Biology. 1999. *

Notes

External links

World Polychaeta Database

Special issue of ''Marine Ecology''
dedicated to polychaetes

a guide to the marine zooplankton of south eastern Australia

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history scientific collection, collections that include current and historical records of animals, plants, Fungus, fungi, ecosystems, geology, paleo ...

{{Authority control * Extant Cambrian first appearances Paraphyletic groups

Description

Internal anatomy and physiology

Ecology

Notable polychaetes

Reproduction

Fossil record

Taxonomy and systematics

See also

References

Bibliography

Notes

External links