Polychaeta () is a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

of generally

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 ...

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 ...

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

s, 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; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

that bear many bristles, called

chaeta A chaeta or cheta (from Greek χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates such ...

e, which are made of

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

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

, to forms which tolerate the extremely high temperatures near

hydrothermal vent A hydrothermal vent is a fissure 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 hotspo ...

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

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

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 deepest-known point of the seabed of Earth, with a depth of by direct measurement from deep-diving submersibles, remotely operated underwater vehicles and benthic landers, and (sometimes) slightly more by sonar bathym ...

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

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

or even luminescent. 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 surfaces. Bundles of bristles, called

e, project from the parapodia. However, polychaetes vary widely from this generalised 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 resources and competitors (for ...

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 (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

life, tube-dwelling or boring, commensalism, and

parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

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

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) t ...

, 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. The head also includes a pair of antennae, tentacle-like palps, and a pair of pits lined with

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 proje ...

, known as "nuchal organs". These latter appear to be chemoreceptors, 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 one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

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 mes ...

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, and ...

. 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's 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 (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...

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 mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

. 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 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 ar ...

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, but some groups have

haemerythrin Hemerythrin (also spelled haemerythrin; grc, αἷμα, haîma, blood, grc, ἐρυθρός, erythrós, red) is an oligomeric protein responsible for oxygen (O2) transport in the marine invertebrate phyla of sipunculids, priapulids, brachiop ...

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 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 are both sympathe ...

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 Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thy ...

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

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

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

. The cuticle is constructed from cross-linked fibres of

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

and may be 200 nm to 13 mm thick. Their jaws are formed from

sclerotised Sclerotin is a component of the cuticle of various Arthropoda, most familiarly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, a form of tanning in which qu ...

collagen, and their

setae In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...

from sclerotised

Ecology

Polychaetes 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 commensals. A few are parasitic. The mobile forms (Errantia) tend to have well-developed sense organs and jaws, while the stationary forms (Sedentaria) lack them, but may have specialized gills or tentacles used for respiration and deposit or filter feeding, e.g., fanworms. 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'', the Pompeii worm, is a species of deep-sea polychaete worm (commonly referred to as "bristle worms"). It is an extremophile found only at hydrothermal vents in the Pacific Ocean, discovered in the early 1980s off the Gal� ...

(''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'', 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 (8CH4·46H2O), 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 amou ...

deposits. *'' Lamellibrachia luymesi'' is a

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

tube worm that reaches lengths of over 3 m and may be the most long-lived animal, 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 ('' Eunice aphroditois'') is a predatory species that can achieve a length at ), with an average diameter of . *''Dimorphilus gyrociliatus'', which has the smallest known genome of any annelid. The species shows an extreme

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

, with females measuring just ~1 mm long and has a simplified segmented body with only six segments, reduced coelom, and no appendages, parapodia or chaetae. The males are only 50 µm long, consist of just a few hundred cells, lack a digestive system, only live for about a week and has just 68 neurons.

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 mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...

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

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

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 (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...

, but most fertilize their eggs externally. The fertilized eggs typically hatch into trochophore larvae, which float among the

, and eventually metamorphose 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, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throu ...

. The rear end of the worm develops into a "stolon" containing the eggs or sperm; this stolon then becomes detached from the parent worm and rises 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 Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the east shore of J.P. Koch F ...

Lagerstätte A Lagerstätte (, from '' Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...

, 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 approxim ...

(early

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

). The oldest found is Phragmochaeta canicularis. Many of the more famous Burgess Shale organisms, such as '' Canadia'', may also have polychaete affinities. '' Wiwaxia'', long interpreted as an annelid, is now considered to represent a mollusc. An even older fossil, '' Cloudina'', dates to the terminal

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

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 scolecodonts, and the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

ized tubes that some of them secrete. Most important

biomineralising polychaetes Biomineralising polychaetes are polychaetes that biomineralize. The most important biomineralizing polychaetes are serpulids, sabellids and cirratulids. They secrete tubes of calcium carbonate. Serpulids have most advanced biomineralizatio ...

are serpulids, sabellids, and cirratulids. Polychaete cuticle does have some preservation potential; 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 and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbre ...

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 oligochaetes (

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

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

Siboglinidae Siboglinidae is a family of polychaete annelid worms whose members made up the former phyla Pogonophora and Vestimentifera (the giant tube worms). The family is composed of about 100 species of vermiform creatures which live in thin tubes buried ...

. 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''; plural 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 nam ...

have been subject to

cladistic Cladistics (; ) 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 typically shared derived char ...

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 ''problematica'' is a term used for a 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, uncertain ...

'' **Family Diurodrilidae **Family Histriobdellidae **Family Nerillidae **Family

Parergodrilidae Parergodrilidae is an enigmatic family of polychaetes with only two genera, one living on the coast, the other terrestrial. They share much in common with the clitellates, but molecular data place them with Questa and Orbiniidae Orbiniidae i ...

**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) *'' S ...

**Family

Protodriloididae ''Protodriloides'' is a genus of polychaete 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 be ...

**Family Saccocirridae **Order Haplodrili **Order Myzostomida ***Family Endomyzostomatidae ***Family Asteromyzostomatidae ***Family Myzostomidae *Subclass Palpata **Family

Protodrilidae Protodrilidae is a family of polychaetes 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 bear ...

**Family Polygordiidae *Subclass Aciculata **Family

Levidoridae Syllidae is a family of small to medium-sized polychaete worms. Syllids are distinguished from other polychaetes by the presence of a muscular region of the anterior digestive tract known as the ''proventricle''. Syllid worms range in size from ...

**Order

Amphinomida Amphinomida is an order of marine polychaetes. The order contains two families: * ''Amphinomidae'' Lamarck, 1818 * ''Euphrosinidae The Euphrosinidae are a family of polychaete worms. The name is from Greek ''Euphrosyne'', meaning merriment; s ...

***Family Amphinomidae ***Family Euphrosinidae **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 muco ...

***Family

Dorvilleidae Dorvilleidae is a family of polychaetes 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 bear ...

***Family Eunicidae ***Family

Hartmaniellidae Hartmaniellidae is a family of polychaetes belonging to the 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 peris ...

***Family Ichthyotomidae ***Family Lumbrineridae ***Family

Oenonidae Oenonidae is a family of polychaetes belonging to the 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 ...

***Family Onuphidae **Order Phyllodocida ***Suborder Aphroditiformia ****Family

Acoetidae Acoetidae is a family of polychaete worms in the subclass Aciculata. Genera * '' Acoetes'' Audouin & Milne Edwards, 1832 * '' Euarche'' Ehlers, 1887 * '' Eumolpe'' * '' Eupanthalis'' McIntosh, 1876 * '' Eupolyodontes'' Buchanan, 1894 * '' Eup ...

****Family

Aphroditidae Aphroditidae is a family of annelids 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 cr ...

****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 cr ...

****Family Polynoidae ****Family

Sigalionidae Sigalionidae 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 ...

***Suborder Glyceriformia ****Family Glyceridae ****Family Goniadidae ****Family

Lacydoniidae Lacydoniidae is a family of polychaetes belonging to the order Phyllodocida. Genera: * '' Lacydonia'' Marion, 1874 References Polychaetes {{Annelid-stub ...

****Family Paralacydoniidae ***Suborder Nereidiformia ****Family Antonbruunidae ****Family Chrysopetalidae ****Family Hesionidae ****Family Nereididae ****Family Pilargidae ****Family

Syllidae Syllidae is a family of small to medium-sized polychaete worms. Syllids are distinguished from other polychaetes by the presence of a muscular region of the anterior digestive tract known as the ''proventricle''. Syllid worms range in size from ...

***Suborder Phyllodocida incertae sedis ****Family Iospilidae ****Family Nautiliniellidae ****Family

Nephtyidae Nephtyidae is a family of polychaete worms. They are commonly referred to as catworms. Characteristics Nephtyidae are pale, clearly segmented polychaetes with a small pentagonal prostomium The prostomium (From Ancient Greek, meaning "before th ...

****Family Typhloscolecidae ****Family Tomopteridae ***Suborder Phyllodociformia ****Family Alciopidae ****Family Lopadorhynchidae ****Family Phyllodocidae ****Family Pontodoridae *Subclass

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 siste ...

**Family Chaetopteridae **Infraclass Canalipalpata ***Order Sabellida ****Family Caobangidae ****Family Fabriciidae ****Family Oweniidae ****Family Sabellariidae ****Family Sabellidae ****Family Serpulidae ****Family

(formerly the phyla Pogonophora & Vestimentifera) ***Order Spionida ****Suborder Spioniformia *****Family

Apistobranchidae Apistobranchidae is a family of polychaetes belonging to the order Spionida Spionida is an order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the littoral or neritic zone ...

*****Family

Longosomatidae Longosomatidae is a family of polychaetes belonging to the order Spionida Spionida is an order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the littoral or neritic zone ...

*****Family

Magelonidae Magelonidae is a family of annelids belonging to the order Spionida Spionida is an order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the littoral or neritic zones. Chara ...

*****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 a ...

*****Family Spionidae *****Family Trochochaetidae *****Family

Uncispionidae Uncispionidae is a family of polychaetes belonging to the order Spionida Spionida is an order of marine polychaete worms in the infraclass Canalipalpata. Spionids are cosmopolitan and live in soft substrates in the littoral or neritic zones. ...

***Order Terebellida ****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. Description Cirratulids vary in ...

(sometimes placed in Spionida) *****Family

Ctenodrilidae Ctenodrilidae is a family of polychaetes belonging to the order Terebellida Terebellida make up an order of the Polychaeta class, commonly referred to as "bristle worms". Together with the Sabellida, the Spionida and some enigmatic familie ...

(sometimes own suborder Ctenodrilida) *****Family Fauveliopsidae (sometimes own suborder Fauveliopsida) *****Family Flabelligeridae (sometimes suborder Flabelligerida) *****Family Flotidae (sometimes included in Flabelligeridae) *****Family

Poeobiidae Flabelligeridae is a family of polychaete worms, known as bristle-cage worms, notable for their cephalic cage: long slender chaetae forming a fan-like arrangement surrounding the eversible (able to be turned inside-out) head. Unlike many polychae ...

(sometimes own suborder Poeobiida or included in Flabelligerida) *****Family Sternaspidae (sometimes own suborder Sternaspida) ****Suborder Terebellomorpha *****Family

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 conta ...

*****Family

Ampharetidae Ampharetidae are a family of terebellid "bristle worm" (class Polychaeta). As such, they belong to the order Canalipalpata, one of the three main clades of polychaetes. They appear to be most closely related to the peculiar alvinellids (Alvin ...

*****Family

Pectinariidae Pectinariidae, or the trumpet worms or ice cream cone worms, are a family of marine polychaete worms that build tubes using grains of sand roughly resembling ice cream cones or trumpets. These structures can be up to long. The earliest pectina ...

*****Family

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 ...

*****Family Trichobranchidae **Infraclass Scolecida ***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 ***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 Hartman and some further revisions ...

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

Capitellida Capitellida is an order of annelids belonging to the class Polychaeta. Families: * Arenicolidae Johnston, 1835 * Capitellidae Capitellidae is a polychaete worm family in the subclass Scolecida. Genera * '' Abyssocapitella'' * '' Amastigos ...

(

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 s ...

) ***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 " archianne ...

(nomen dubium) ***Order Questida (nomen dubium) ***Order Scolecidaformia (nomen dubium) *Subclass Echiura ** Order Bonelliida *** Family

Bonelliidae Bonelliidae is a family of marine worms (Class Echiura, phylum Annelida) noted for being sexually dimorphic, with males being tiny in comparison with the females. They occupy burrows in the seabed in many parts of the world's oceans, often at gr ...

*** Family Ikedidae ** Order

Echiurida Echiurida is a suborder of the order Echiuroidea, an order of polychaete worms. Families The following families are classified within the suborder: * Echiuridae Quatrefages, 1847 * Thalassematidae Forbes ''Forbes'' () is an American ...

*** Family Echiuridae *** Family Thalassematidae *** Family

Urechidae Urechidae (commonly known as "fat innkeeper" or "penis fish") is a family of spoonworms in the subclass Echiura. The only genus in the family is ''Urechis'', which has four species. Species The World Register of Marine Species includes these sp ...

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 collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

{{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