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

, where they are paired, unjointed

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

outgrowths that bear the

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. In several groups of

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the a ...

s and

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary tim ...

s, 'parapodium' refers to lateral fleshy protrusions. __TOC__

Annelid parapodia

Most species of polychaete annelids have paired, fleshy parapodia which are segmentally arranged along the body axis. Parapodia vary greatly in size and form, reflecting a variety of functions, such as gas exchange, anchorage, protection and locomotion.

General description

Parapodia in

polychaetes 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 made ...

can be

uniramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plu ...

(consisting of one lobe or ramus) but are usually

biramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plu ...

(two lobes or rami). In the latter case, the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

lobes are called notopodia and the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

lobes neuropodia. Both neuropodia and notopodia may possess a bundle of chaetae (neurochaetae and notochaetae respectively), which are highly specific and greatly diversified. A single stout internal chaeta, called an acicula, may be present in each lobe, which are used to support well-developed parapodia. Notopodia and neuropodia can also bear cirri which are tentacle-like projections of the parapodia. In some groups, such as the scale worms (e.g. Polynoidae), the dorsal cirrus is modified into a scale (or

elytron An elytron (; ; , ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometimes alterna ...

). In most species, the anteriormost segments may be specialised into the head region and

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 ...

, which can result in the modification of those parapodia, loss of chaetae and elongation of the cirri into anterior-facing tentacular cirri.

Glossary of components of the parapodium

Gastropod parapodia

The fleshy protrusions on the sides of some marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s are also called parapodia. They are particularly well-developed in

sea butterflies Sea butterflies, scientific name Thecosomata (thecosomes, "case / shell-body"), are a taxonomic suborder of small pelagic swimming sea snails. They are holoplanktonic opisthobranch gastropod mollusks. Most Thecosomata have some form of calcifi ...

. Some sea hares use their parapodia to swim. Parapodia can even be used for respiration (similar to gills) or for locomotion. Parapodia are found in the following taxonomic groups of gastropods: * Clade

Cephalaspidea The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia.Jörger K. M., Stöger I., Kano Y., Fukuda H., ...

* Clade

Thecosomata Sea butterflies, scientific name Thecosomata (thecosomes, "case / shell-body"), are a taxonomic suborder of small pelagic swimming sea snails. They are holoplanktonic opisthobranch gastropod mollusks. Most Thecosomata have some form of calcifi ...

* Clade

Gymnosomata Sea angels (clade Gymnosomata) are a large group of small free-swimming sea slugs, not to be confused with Cnidarians (Jellyfish and other similar creatures), classified into six different families. They are pelagic opisthobranchs in the clade Gy ...

* Clade Aplysiomorpha

References

{{reflist Annelid anatomy Gastropod anatomy

Annelid parapodia

General description

Glossary of components of the parapodium

Gastropod parapodia

See also

References