Editing Parapodium

{{Short description|Protusions from the body in invertebrates}}
{{For|the genus of plants|Parapodium (plant)}}
[[File:L oculatus para wscale.jpg|thumb|Specimen of the annelid, [[Lepidonotus|''Lepidonotus oculatus'']], with a microscope image of one of its parapodia (inset). [[Museums Victoria]] specimen.]]
In invertebrates, the term '''parapodium''' ([[Greek language|Gr.]] ''para'', beyond or beside + ''podia'', feet; {{plural form}}: '''parapodia''') refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in [[Annelid|annelids]], where they are paired, unjointed [[Anatomical terms of location#Directional terms|lateral]] outgrowths that bear the [[chaeta]]e. In several groups of [[sea snail]]s and [[sea slug]]s, 'parapodium' refers to lateral fleshy protrusions.
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==Annelid parapodia==
[[File:Annelid parapodium anatomy.jpg|thumb|upright=0.8|An image plate showing the different anatomical features (dashed outline) of a representative annelid parapodium. Parapodium is from [[Lepidonotus|''Lepidonotus oculatus'']] and is a Museums Victoria specimen.]]
[[File:Arctonoe sp. parapodium with chaetae labels.png|upright=1.5|thumb|Microscope photograph of a parapodium from a specimen of ''[[Arctonoe]]'' sp. showing the internal acicula that support the two lobes of the parapodium. This parapodium is from a Museums Victoria specimen.]]
Most species of [[Polychaete|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, anchorage, protection and locomotion.<ref>{{cite book |last1=Rouse |first1=Greg |last2=Pleijel |first2=Frederick |title=Polychaetes |date=2001 |publisher=Oxford University Press |location=Oxford |isbn=0198506082}}</ref>

===General description===
Parapodia in [[polychaetes]] can be [[uniramous]] (consisting of one lobe or ramus) but are usually [[biramous]] (two lobes or rami). In the latter case, the [[Dorsum (biology)|dorsal]] lobes are called notopodia and the [[ventral]] lobes neuropodia. Both neuropodia and notopodia may possess a bundle of [[Chaeta|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 [[Cirrus (biology)|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 (Annelida)|elytron]]). <ref>{{cite book |last1=Hutchings |first1=P. A. |last2=Fauchald |first2=K. |title=Polychaetes and Allies: the Southern Synthesis - Class Polychaeata: Definition and General Description |date=2000 |publisher=CSIRO Publishing |location=Melbourne |pages=1–3}}</ref>

In most species, the anteriormost segments may be specialised into the head region and [[prostomium]], 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===
{| class="wikitable"
|-
! Component !! Description
|-
| '''Dorsal cirrus''' || [[Cirrus (biology)|Cirrus]] extending from the notopodium; can be modified into a [[Elytron (Annelida)|scale]] (or elytron) in scale worms.
|-
| '''Neuroaciculum''' || Stout internal supporting chaeta ([[acicula]]) for the neuropodium
|-
| '''Neurochaetae''' || [[Chaeta|Chaetae]] of the neuropodium 
|-
| '''Neuropodium''' || Ventral lobe
|-
| '''Notoaciculum''' || Stout internal supporting chaeta ([[acicula]]) for the notopodium
|-
| '''Notochaetae''' || [[Chaeta|Chaetae]] of the notopodium 
|-
| '''Notopodium''' || Dorsal lobe
|-
| '''Ventral cirrus''' || [[Cirrus (biology)|Cirrus]] extending from the neuropodium
|}
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==Gastropod parapodia==
[[File:Plakobranchus ocellatus 3.png|thumb|left|upright=0.5|Dorsal view of a freshly collected intact sea slug, ''[[Plakobranchus ocellatus]]'', showing its head, [[rhinophore]]s and parapodia.]]
The fleshy protrusions on the sides of some marine [[gastropod]]s are also called parapodia. They are particularly well-developed in [[sea butterflies]]. 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]]
* Clade [[Thecosomata]]
* Clade [[Gymnosomata]]
* Clade [[Aplysiomorpha]]
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==See also==
*[[Epitoke parapodium]]
*[[Annelida]]

==References==
{{reflist}}



[[Category:Annelid anatomy]]
[[Category:Gastropod anatomy]]