Scolecida is an

infraclass In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, king ...

of polychaete worms. Scolecids are mostly unselective

deposit feeders Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebr ...

on marine detritus.

Characteristics

Scolecids have

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 ...

with rami that are all alike. The

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 distinct. The head has no

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including ante ...

s or palps and is usually conical, though in the Scalibregmatidae, it has a "T"-shaped tip, and in Paraonidae, there is a single, central antenna. In some families there are sometimes some tiny eyespots. The oesophagus is evertable forming a sac-like proboscis which may have several finger-like lobes. The anterior segments and their appendages are all similar. The notopodia and neuropodia consist of unbranched capillary

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, sometimes with hooks. There is a single central gill in Cossuridae on an anterior segment and simple segmental gills are present in some other families.Annelida.net
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Systematics

The families Arenicolidae, Capitellidae and Maldanidae were formerly part of the order Capitellida. They are now included in infraclass Scolecida along with Cossuridae, Orbiniidae, Opheliidae, Paraonidae and Scalibregmatidae. This

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 ter ...

is probably not a natural grouping and is likely to be revised in the future.

Subdivisions

**Family Aeolosomatidae **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

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 Questidae **Family Scalibregmatidae

References

{{Taxonbar, from=Q549978 Polychaetes