Parapodia and setae

Biramous parapodia

Definition: Parapodia are paired, lateral appendages extending from the body segements. A parapodium is basically biramous or uniramous, consisting of the upper division called the notopodium and a ventral division called the neuropodium.

uniramous with one branch

biramous with two branches

biramous parapodia showing the notopodium(upper division) and neuropodium(lower division).

Definitions: Biramous parapodia: parapodia with two branches, the neuropodium(lower division) and the notopodium(upper division) Uniramous parapodia: parapodia with a single branch. The notopodium is absent. Sub-biramous parapodia: parapodia with neuropodium well developed and notopodium reduced. Reduced means it is biramous but both neuropodium and notopodium of the setae are small.

Here are the various types of parapodia modified for different functions along the polychaetes families. This type of parapodia and setae are modified for a burrowing polychaete. This type of parapodia and setae are modified for a tube dwelling polychaete. The jointed setae is modified for a crawling polychaete such as spionid in fouling communities. The hooded hooked setae is modified for a sedentary polychaete.

The nereids, phyllodocids and hesionids have well-developed parapodia and setae to crawl over surfaces rapidly. The sedentary polychaetes have reduced parapodia. They are tubiculous and occupy simple vertical or U-shaped burrows excavated in substratums. The parapodial lobes contain setal sacs from which the setae project. The setae assume a variety of shapes and in some species, the setal bundles may contain more one type of setae. New setae are continually produced as old ones are lost.

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