Sedentaria is a diverse

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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

. It is traditionally treated as a subclass of the paraphyletic class

Polychaeta 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 many bristles, called chaetae, which are m ...

, but it is also a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

group uniting several

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 ...

s and the monophyletic class

Clitellata 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, the ...

. It is the sister group of

Errantia Errantia is a diverse group of marine polychaete worms in the phylum Annelida. Traditionally a subclass of the paraphyletic class "Polychaeta", it is currently regarded as a monophyletic group within the larger Pleistoannelida, composed of Er ...

Phylogeny

The phylogeny of

s is slowly being resolved. Sedentaria and

are the two biggest

s of polychaetes, and together they compose clade

Pleistoannelida Pleistoannelida is a group of annelid worms that comprises the vast majority of the diversity in phylum Annelida. Discovered through phylogenetic analyses, it is the largest clade of annelids, comprised by the last common ancestor of the highly div ...

. Sedentaria's most basal clade is

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 ...

. Other groups that are nested within Sedentaria are:

, 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 p ...

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. Characteristics Spionids have a single pair of flexible feeding tentacles w ...

clade,

Opheliida Opheliida is an order of polychaetes belonging to the class Polychaeta. Families: * Opheliidae Malmgren, 1867 * Scalibregmatidae Malmgren, 1867 References

Polychaetes {{annelid-stub ...

Echiura The Echiura, or spoon worms, are a small group of marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into segments, but echiurans have secondarily lo ...

, Cirratuliformia,

Terebelliformia Terebelliformia is a group 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 bear m ...

Maldanomorpha Maldanomorpha is a monophyletic group, or clade, of polychaete worms in the phylum Annelida. Several phylogenetic analyses based on morphology (biology), morphological and molecular phylogeny, molecular data have shown that this clade unites the f ...

and the families

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 ...

and

Capitellidae Capitellidae is a polychaete worm family in the subclass Scolecida. Genera * ''Abyssocapitella'' * ''Amastigos'' * ''Anotomastus'' * ''Baldia (worm), Baldia'' * ''Barantolla'' * ''Branchiocapitella'' * ''Capitella'' * ''Capitellethus'' * ''Cap ...

. Some

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 ...

, such as

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 ...

and

Myzostomida The Myzostomida or Myzostomatida are an order of small marine worms, which are parasitic on echinoderms, mostly crinoids. These highly unusual and diverse annelids were first discovered by Friedrich Sigismund Leuckart in 1827. Morphology A ...

, are still difficult to place due to their long branching, but they likely belong to either

or Sedentaria.

References

{{taxonbar, from=Q9373141 Polychaetes Annelids