Citizendia
Your Ad Here

Polychaetes
Fossil range: Cambrian (or earlier?) - present
"A variety of marine worms": plate from Das Meer by M. J. Schleiden (1804–1881).
"A variety of marine worms": plate from Das Meer by M. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with J. Schleiden (1804–1881).
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Polychaeta
Grube, 1850
Subclasses

Palpata
Scolecida

The Polychaeta or polychaetes are a class of annelid worms, generally marine. The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising A class is the Taxonomic rank in the Biological classification of organisms in Biology below phylum and above order. The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Parapodia ( Gr para, beyond or beside + podia, feet singular parapodium, are paired un-jointed Lateral outgrowths A chaeta or cheta (see spelling differences) is a Chitinous bristle or Seta found on Annelid worms such as the Earthworm Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine Indeed the polychaetes are sometimes referred to as bristle worms. More than 10,000 species are described in this class. Common representatives include the lugworm (Arenicola marina) and the sandworm or clam worm Nereis. The lugworm or sandworm is a large marine worm of the phylum Annelida. The Common clam worm ( Nereis succinea) is a widely distributed Polychaete worm

Contents

Anatomy and physiology

The polychaetes' paddle-like and highly vascularized parapodia are used for movement and act as the annelid's primary respiratory surfaces (parapodia can be thought of as kinds of external gills that are also used for locomotion). The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising Gas exchange or respiration takes place at a respiratory surface—a boundary between the external environment and the interior of the body A gill is an anatomical structure found in many aquatic organisms Polychaeta also have well-developed heads compared to other annelids.

General anatomy of a polychaete
General anatomy of a polychaete
Tomopteris from plankton
Tomopteris from plankton

Ecology

Polychaetes are extremely variable in both form and lifestyle and include a few taxa that swim among the plankton. Tomopteris (Neo-Latin from Greek meaning "a cut" + "wing" but taken to mean "fin" is a genus of marine Planktonic Polychaete Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Most burrow or build tubes on the bottom, and some live as commensals. In Ecology, commensalism is a kind of symbiotic relationship between two organisms where one benefits and the other is not significantly harmed or helped (like a bird A few are parasitic. The mobile forms or Errantia tend to have well-developed sense organs and jaws, while the Sedentaria (or stationary forms) lack them but may have specialized gills or tentacles used for respiration and deposit or filter feeding, e. g. , fanworms.

A few groups have evolved to live in terrestrial environments, like Namanereidinae with many terrestrial species, but are restricted to humid areas. Some have even evolved cutaneous invaginations for aerial gas exchange.

Sabellastarte indica
Sabellastarte indica

One notable polychaete, the Pompeii worm (Alvinella pompejana) is endemic to the hydrothermal vents of the Pacific Ocean. The Pompeii worm ( Alvinella pompejana) is a deep-sea Polychaete vermiform Extremophile found only at Hydrothermal vents A hydrothermal vent is a Fissure in a planet's surface from which geothermally heated Water issues The Pacific Ocean is the largest of the Earth 's Oceanic divisions Pompeii worms are thought to be the most heat-tolerant complex animals known.

A recently discovered genus Osedax includes the Bone-eating snot flower. Osedax is a Genus of deep-sea Siboglinid Polychaetes commonly called zombie or bone-eating worms first discovered in Monterey Bay Osedax is a Genus of deep-sea Siboglinid Polychaetes commonly called zombie or bone-eating worms first discovered in Monterey Bay

Another remarkable polychaete is Hesiocaeca methanicola, which lives on methane clathrate deposits. Methane clathrate deposits in the ocean floor have been found to be inhabited by Polychaete worms of the species Hesiocaeca methanicola. Methane clathrate, also called methane hydrate or methane ice, is a solid form of water that contains a large amount of Methane within its Crystal

Lamellibrachia luymesi is a cold seep tube worm that reaches lengths of over 3 meters and may be the most long lived animal at over 250 years old. Lamellibrachia is a genus of tube worms related to the Giant tube worm, Riftia pachyptila. A cold seep (sometimes called a cold vent) is an area of the Ocean floor where Hydrogen sulfide, Methane and other Hydrocarbon -rich

Evolutionary history

The oldest crown group polychaetes fossils come from the Sirius Passet L:agerstatte, which is tentatively dated to the lower-middle Atdabanian (early Cambrian). Sirius Passet is a Cambrian Lagerstätte in Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland [1] Many of the more famous Burgess Shale organisms, such as Canadia and Wiwaxia, may also have polychate affinites. See also Burgess shale type fauna The Burgess Shale is famous for the exceptional preservation of the fossils found within it in which the soft parts are preserved See also Halwaxiida Wiwaxia is genus of soft-bodied scale-covered animals known from Burgess shale type dating from the Early to Middle Cambrian An even older fossil, Cloudina, dates to the terminal Ediacaran period; this has been interpreted as an early polychaete, although consensus is absent. The Cloudinids, early Metazoan family containing the Genus Cloudina, lived in the late Ediacaran period and The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic [2]

Being soft bodied, the fossil record of polychaetes is dominated by their fossilized jaws, known as scolecodonts, and the mineralized tubes that some of them secrete. A scolecodont is the jaw of a polychaete annelid, a common type of Fossil -producing Segmented worm useful in Invertebrate A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific

Taxonomy and systematics

Taxonomically, the polychaetes are thought to be paraphyletic, meaning that as a group it contains its most recent common ancestor, but does not contain all the descendants of that ancestor. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all Groups that may be descended from the polychaetes include the earthworms, the leeches, sipunculans, and echiurans. Earthworm is the usual name for the largest members of Oligochaeta (which is either a class or subclass depending on the author in the phylum Annelida In classical Leeches are Annelids comprising the Subclass Hirudinea. There are freshwater terrestrial and marine leeches The Sipuncula or Sipunculida, sipunculid worms or peanut worms, are a phylum containing 144-320 Species (estimates vary of bilaterally The Echiura, or spoon worms are a small group of marine Animals They are often considered to be a group of Annelids although they lack the segmented The Pogonophora and Vestimentifera were once considered separate phyla, but are now classified in the polychaete family Siboglinidae. Siboglinidae, also known as the beard worms, is a family of Polychaete annelid worms whose members made up the former phyla Siboglinidae, also known as the beard worms, is a family of Polychaete annelid worms whose members made up the former phyla

Much of the classification below matches Rouse & Fauchald, 1998, although that paper does not apply ranks above family.

Older classifications recognize many more (sub)orders than the layout presented here. As comparatively few polychaete taxa have been subject to cladistic analysis, some groups which are usually considered invalid today may eventually be reinstated. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to Cladistics is the hierarchical classification of Species based on evolutionary ancestry

See also

References

  1. ^ Conway Morris, S. and Peel, J. S. 2008. The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet Lagerstätte, Peary Land, North Greenland. Acta Palaeontologica Polonica 53 (1): 137–148.
  2. ^ Miller, A. J. (2004), A Revised Morphology of Cloudina with Ecological and Phylogenetic Implications, <http://ajm.pioneeringprojects.org/files/CloudinaPaper_Final.pdf>. Retrieved on 24 April 2007 

External links

Dictionary

polychaete

-noun

  1. Alternative spelling of polychete.
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic