Errantia is a diverse group of marine

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

worms in the phylum

Annelida 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, and leeches. The species exist in and have adapted to variou ...

. Traditionally a subclass of the

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 Polychaeta, it is currently regarded as a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

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 di ...

, 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 sis ...

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

Phylogeny

The

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

s is slowly being resolved. Errantia and

are the two biggest

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s of polychaetes, and together they compose clade

. Two groups are nested within Errantia:

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 ...

( Eunicida + Phyllodocida) 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 histor ...

(

small Small means of insignificant size Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to three geometrical measures: length, area, or ...

meiofaunal worms such as the Protodrilida). Historically, the order Amphinomida was part of this subclass. However,

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

place Amphinomida 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 marine annelid worms, that have secondarily lost their segmentation. Sipuncula was once considered a phylum of unsegmented ...

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''; : 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 ...

, such as Spintheridae and

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 ...

, 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 " Polychaeta". In 1977 the zoologist Kristian Fauchald split Errantia into three orders: Phyllodocida, Amphinomida and Eunicida, giving way to this classification. *Order Amphinomida – 2 families ( Amphinomidae, Euphrosinidae) *Order Eunicida **Superfamily Eunicea – 7 families ( Onuphidae, Eunicidae, Lumbrineridae, Iphitimidae, Arabellidae, Lysaretidae, Dorvilleidae) **Superfamily incertae sedis – 2 families ( Histriobdellidae, Ichthytomidae) *Order Phyllodocida **Suborder Phyllodociformia – 4 families ( Phyllodocidae, Alciopidae, Lopadorrhynchidae, 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 elongated rost ...

, Pholoididae, Eulepethidae, Sigalionidae) ***Superfamily Chrysopetalacea – 2 families ( Chrysopetalidae, Palmyridae) ***Superfamily Pisionacea – 1 family ( Pisionidae) **Suborder Nereidiformia – 6 families ( Hesionidae, Pilargiidae, Syllidae, Calamyzidae, Nereididae, Antonbmunidae) **Suborder Glyceriformia – 3 families ( Glyceridae, Goniadidae, Lacydoniidae) **Suborder incertae sedis – 5 families ( Iospilidae, Nephtyidae, Sphaerodoridae, Tomopteridae, Typhloscolecidae)

References

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