Parapodium

Source: Wikipedia, the free encyclopedia.
For the genus of plants, see Parapodium (plant).
Specimen of the annelid, Lepidonotus oculatus, with a microscope image of one of its parapodia (inset). Museums Victoria specimen.

In invertebrates, the term parapodium (Gr. para, beyond or beside + podia, feet; pl.: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed lateral outgrowths that bear the chaetae. In several groups of sea snails and sea slugs, 'parapodium' refers to lateral fleshy protrusions.

Annelid parapodia

An image plate showing the different anatomical features (dashed outline) of a representative annelid parapodium. Parapodium is from Lepidonotus oculatus and is a Museums Victoria specimen.
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 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.[1]

General description

Parapodia in

elytron). [2]

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

Component Description
Dorsal cirrus
scale
(or elytron) in scale worms.
Neuroaciculum Stout internal supporting chaeta (acicula) for the neuropodium
Neurochaetae Chaetae of the neuropodium
Neuropodium Ventral lobe
Notoaciculum Stout internal supporting chaeta (acicula) for the notopodium
Notochaetae Chaetae of the notopodium
Notopodium Dorsal lobe
Ventral cirrus Cirrus extending from the neuropodium

Gastropod parapodia

Dorsal view of a freshly collected intact sea slug, Plakobranchus ocellatus, showing its head, rhinophores and parapodia.

The fleshy protrusions on the sides of some marine

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

See also

  • Epitoke parapodium
  • Annelida

References

  1. ISBN 0198506082
    .
  2. ^ Hutchings, P. A.; Fauchald, K. (2000). Polychaetes and Allies: the Southern Synthesis - Class Polychaeata: Definition and General Description. Melbourne: CSIRO Publishing. pp. 1–3.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Parapodium&oldid=1184417350"