Phyllodocida is an order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of polychaete

Polychaete

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...

 worms in the subclass

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Aciculata

Aciculata

Aciculata is an order of polychaete worms. These worms are found worldwide in marine environments and brackish water.-Families:Suborder Eunicida*Amphinomidae Savigny in Lamarck, 1818 *Diurodrilidae Kristensen and Niilonen, 1982...

. 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 cracks and crevices in bedrock. A few construct tubes in which they live and some are pelagic, swimming through the water column. There are estimated to be about 3,500 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 in the order.

Characteristics

Phyllodocida are segmented

Segmentation (biology)

Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...

 worms and range in size from a few millimetres long to over a metre. Each segment bears a pair of paddle-like parapodia

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

. The prostomium

Prostomium

Prostomium is the first body segment in annelid worms. It is in front of the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. It sometimes bears antennae and eyes. It often functions like a kind of overlip when the animal is feeding...

 generally has one or two pairs of eyes, a dorsal pair of antennae

Antenna (biology)

Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

, a ventral pair of sensory palps

Pedipalp

Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...

 and a pair of organs on the neck. The peristomium is a ring, often hidden dorsally by the prostomium and the first segment. There is a muscular proboscis

Proboscis

A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...

 with one or more pairs of jaws. The next few segments tend to differ from those further back in having enlarged dorsal and ventral cirri (fine appendages) and reduced parapodial lobes and chaeta

Chaeta

A chaeta or cheta is a chitinous bristle or seta found on an insect, arthropod or annelid worms such as the earthworm, although the term is also frequently used to describe similar structures in other invertebrates. The plural form is chaetae or chetae.In the Polychaeta, they are located on the...

e (bristles). Some species have appendages with specialised functions but most have many segments that are similar to each other but which vary in size and shape along the length of the body without abrupt changes in the chaetae and parapodia from one to the next.

Phylogenetic relationships

The three main subgroups are Aphroditiformia, Glyceriformia and Nereidiformia. The Aphroditiformia are characterised by the presence of elytrae or scales on alternating segments. The Glyceriformia are characterised by the presence of unique cone-shaped and ringed prostomiums. The Nereidiformia are more problematic, having no universally distinguishing common features. There is agreement on the monophyly

Monophyly

In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

 of a group including the Hesionidae, Nereididae and Chrysopetalidae families but opinions differ about Pilargidae, and molecular and morphological studies continue.

Families

Recognised families:

Suborder Aphroditiformia

Superfamily Aphroditoidea

Acoetidae

Aphroditidae

Eulepethidae

Pholoidae

Polynoidae

Polynoidae

A family of scaled Polychaete worms known as the "scale worms". Short and flat, specimens reach as much as 20 cm in length and 10 cm width. An almost-constant number of small segments is the norm. They are covered by scales, technically termed elytra....

Sigalionidae

Superfamily Chrysopetalacea

Chrysopetalidae

Superfamily Pisionacea

Pisionidae

Suborder Glyceriformia

Glyceridae

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 ferocious epi- and infaunal polychaetes that prey upon small...

Goniadidae

Lacydoniidae

Paralacydoniidae

Suborder Nereidiformia

Antonbruuniidae

Hesionidae

Hesionidae

Hesionidae are a family of phyllodocid "bristle worms" . They are marine organisms. Most are found on the continental shelf; Hesiocaeca methanicola is found on methane ice, where it feeds on bacterial biofilms.A characteristic apomorphy of the Hesionidae are the cirrophores of the anterior...

Nereidae

Nereidae

Nereididae are a family of polychaete worms. It contains about 500 – mostly marine – species grouped into 42 genera. They may be commonly called ragworms or clam worms.-Characteristics:...

Pilargidae

Syllidae

Suborder Phyllodocida incertae sedis

Iospilidae

Nephtyidae

Nephtyidae

Nephtyidae is a taxonomic family of 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...

Sphaerodoridae

Tomopteridae

Typhloscolecidae

Yndolaciidae

Suborder Phyllodociformia

Alciopidae

Lopadorhynchidae

Phyllodocidae

Pontodoridae

Incertae sedis

Nautiliniellidae