Errantia is a diverse group of marine

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 many bristles, called chaetae, which are ...

worms in the phylum Annelida. Traditionally a subclass of the

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

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 ...

", it is currently regarded as 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 ...

group within the larger

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 ...

, composed of Errantia and

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 sist ...

. These worms are found worldwide in marine environments and brackish water.

Phylogeny

The

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

s is slowly being resolved. Errantia and

are the two biggest clades of polychaetes, and together they compose clade

. Two groups are nested within Errantia: Aciculata (

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 ...

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 ...

) and

Protodriliformia Protodriliformia is a clade of small marine polychaetes, comprised by the groups of meiofaunal interstitial worms Protodrilida and Polygordiidae, formerly considered " archiannelids". It is the most basal clade of Errantia. Evolutionary history ...

(

small Small may refer to: Science and technology * SMALL, an ALGOL-like programming language * Small (anatomy), the lumbar region of the back * ''Small'' (journal), a nano-science publication * <small>, an HTML element that defines smaller text ...

meiofaunal worms such as the

Protodrilida Protodrilida is an order of polychaetes belonging to the class Polychaeta. Families: * Protodrilidae Czerniavsky, 1881 * Protodriloididae ''Protodriloides'' is a genus of polychaetes belonging to the monotypic family Protodriloididae. The spec ...

). Historically, the order

Amphinomida Amphinomida is an order of marine polychaetes. The order contains two families: * '' Amphinomidae'' Lamarck, 1818 * '' Euphrosinidae'' Williams, 1852 References Polychaetes {{annelid-stub ...

was part of this subclass. However, phylogenetic analyses place

inside a basal clade with

Sipunculida The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms. The name ''Sipuncula'' is from the genus name '' Sipunculus'', and comes from the Latin ...

and '' Lobatocerebrum'', and this clade is the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

. 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 n ...

, such as Spintheridae 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 Errantia or

Classification

Historical

Errantia is, along with

, one of the two old orders of the

class "

". In 1977 the zoologist Kristian Fauchald split Errantia into three orders:

and

, giving way to this classification. *Order

– 2 families ( Amphinomidae, Euphrosinidae) *Order

**Superfamily Eunicea – 7 families ( Onuphidae,

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 cons ...

, Lumbrineridae, Iphitimidae, Arabellidae, Lysaretidae, Dorvilleidae) **Superfamily incertae sedis – 2 families ( Histriobdellidae, Ichthytomidae) *Order

**Suborder Phyllodociformia – 4 families ( Phyllodocidae,

Alciopidae Alciopidae 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 ...

, Lopadorhynchidae, Pontodoridae) **Suborder Aphroditiformia ***Superfamily Aphroditacea – 6 families ( Aphroditidae, Polynoidae,

Polyodontidae Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elongl ...

, Pholoididae, Eulepethidae, Sigalionidae) ***Superfamily Chrysopetalacea – 2 families ( Chrysopetalidae, Palmyridae) ***Superfamily Pisionacea – 1 family ( Pisionidae) **Suborder Nereidiformia – 6 families (

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 o ...

, Pilargiidae, Syllidae, Calamyzidae, Nereidae, Antonbmunidae) **Suborder Glyceriformia – 3 families (

Glyceridae Glyceridae is a family of polychaete worms. They are commonly referred to as beak-thrower worms or bloodworms. They are bright red, segmented, aquatic worms. The proboscis worm '' Glycera'' is sometimes called bloodworm. The Glyceridae are epi- a ...

, Goniadidae,

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

) **Suborder incertae sedis – 5 families ( Iospilidae,

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 with two pairs of small antennae. Their segments are litt ...

, Sphaerodoridae, Tomoptendae, Typhloscolecidae)

References

{{Taxonbar, from1=Q6759542, from2=Q2823177 Protostome subclasses