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Sedentary Sabellidae

Sedentary Sabellidae

without rank: Tissue animals (Eumetazoa)
without rank: Bilateria
without rank: Primordial mouths (protostomia)
Over trunk : Lophotrochozoa (Lophotrochozoa)
Trunk : Annelids (Annelida)
Class : Multi-bristle
Scientific name
Pit , 1850

Polychaete or polychaete (from ancient Greek πολύς polys , much 'and χαίτη Chaite , hair') are a class of annelid worms (Annelida), the plan relative to the second annelid class Clitellata is usually considered relatively pristine. However, the variety of shapes of the multi-bristle is so great that so far no agreement has been reached on which multi-bristle group represents a primitive combination of features. Multi-bristles get their name from the numerous bristles ( Chaetae , also Setae), which serve as supporting elements and locomotion apparatus on each segment.

The well over 10,000 described species are divided into up to 24 orders with over 80 families. On a morphological and molecular biological basis, however, there are currently considerable doubts as to whether the many-bristles form a community of descent ( Monophylum ). If this suspicion is confirmed, the monophyly of annelid worms as a whole must also be questioned.


With a few exceptions, many bristles live in the sea. Here they colonize all habitats, such as the free water body ( pelagic ) as part of the zooplankton , the riparian zones and the permanently water-covered area (sublittoral). On May 31, 2009, the research robot Nereus discovered a multi-bristle in Challenger Deep , the deepest point on earth. There are freely moving (" Errantia ") and sessile species (" Sedentaria "). This subdivision is only functional, but systematically it is outdated.

Way of life

The variety of shapes of the polybristles must be understood in connection with the settlement of diverse habitats. In addition, very different strategies for obtaining food were developed. Some forms are hunters and have large, well-functioning eyes (some with lenses), others are scavengers and substrate eaters or grazers, and still others, especially sedentaria , filter their food from the surrounding water. The tube worms of the species Riftia pachyptila are particularly unusual ; they get their food in the lightless deep sea from symbiotic archaea , which in turn derive their energy chemotrophically from hydrogen sulfide (H 2 S) in the vicinity of hydrothermal springs ( black smokers ). Riftia has no gut.


The Chaetae sit at the Parapodia (Notopodium and Neuropodium) of the Polychaetes .

The group of Nereids is often cited as an example of a typical multi-bristle organization , such as Platynereis dumerilii , a particularly well-researched polychaete species from the Mediterranean, which has also been established as a developmental genetic model organism since the late 1990s.


Multi-bristled animals are primarily segmented animals with a secondary body cavity ( coelom ), but these typical annelid worm features can be lost in very specialized or reduced forms. As a highly primal, group-specific characteristic, the individual segments have paired attachments (parapodia) for locomotion, which are traversed by numerous chitinous bristles. The bristles called Chaetae can be designed as a short shape or as floating bristles and, with their difficultly designed tips, serve as holding or paddling devices. Another bristle is the so-called supporting bristle or acicula, which, depending on the form of the parapodium, supports the parapodia individually or in pairs, as it were as an inner skeleton. Thread- shaped or fringe- shaped appendages are called cirrus (seldom also cirrus), scale-shaped are called elytra. Like all annelids, polychaetes have a hydroskeleton . In contrast to roundworms, however, they have a more flexible and more mobile skin muscle tube: Under the epidermis there is an outer ring and an inner longitudinal muscle layer, which enables complex movements. The mouth opening is covered by the prostomium, in the metastomium. The throat ( pharynx ) is protruding and mostly toothed (especially in predatory species). The intestinal tube runs straight through the segments and ends with the anal opening in the pygidium , the last segment in the rear end of the animals. Another typical feature are the nuchal organs , which are paired chemosensory devices in the head section. A negative feature in comparison to the other traditional class of annelid worms, the clitellata, is the lack of a clitellum .

Respiration and blood vessel system

  • Closed blood vessel system
  • A dorsal vessel and a ventral vessel run through the body in the longitudinal direction and are connected to one another by annular vessels; the dorsal vessel is contractile and acts as a heart.
  • There is a pair of nephridia per segment
  • Gills are often developed for breathing, especially in larger species. These can usually be found as attachments to the parapodia . In the case of smaller species, skin or intestinal breathing is often sufficient; these then have no gills.

Sessile or tube living species have developed behavior in order to supply the oxygen-poor environment with oxygen-rich water through movement, or they have developed special gill structures.


Nervous system and sensory organs

The prostomium (head flap) and peristomium (mouth segment) sit on the head section. There are also the palps (organs of touch), antennae and eyes, which are necessary for finding the food. Chemical sensory organs (nuchal organs) are located on the prostomium. The cephalized "central nervous system" consists of the upper and lower pharyngeal ganglion which are connected to the abdominal marrow via the pharyngeal connector (often a pair of ganglia can be found per segment).

Many bristles and people


The hard bristles easily penetrate human skin and break off easily. This causes burning pain and skin irritation. The bristles are not poisoned and the cause of the burning pain is unknown. In 2008 the natural substance complanin was isolated from Eurythoe complanata , which has an inflammatory effect. In the literature, it is advised to remove the bristles using adhesive tape and to disinfect the affected areas of skin to avoid secondary infections.

Glycera worms can inflict painful bites. They have four grasping tongs that resemble the poisonous fangs of poisonous snakes. With these they inject a poison which is harmless for people who do not react allergically. The pain of the bite is comparable to that of being stung by a honey bee .

Many bristles as food

Multi-bristled bristles are not used as food except for one type. Only the Samoa Palolo , Palola viridis , is important for human nutrition. This worm lives hidden in caves and strangles its abdomen every 353 or 382 days. This carries the sex organs. In this way, large numbers of the abdomen drift to the surface of the water at the same time. This increases the likelihood of a successful pairing. The inhabitants of the South Sea islands, particularly Samoas and the Fiji Islands, fish them as a delicacy before sunrise. They are eaten raw or prepared in various ways.


It was Adolph Eduard Grube who in 1850 was the first to describe the Appendiculata polychaeta as an order to which “those annelids with lateral bristle bundles or bristle combs, which either next to these or on the back or head part, have all sorts of soft appendages, sometimes just lobes, sometimes leaves, threads or carry more complex organs; the bristles stand together (except sometimes at the body ends) at least 8, but usually far more numerous. ”Initially in the rank of an order, later a class, this taxon has remained in the systematics to this day, albeit at the latest since the molecular biological Investigations by Shigeaki Kojima in 1998, the Polychaeta viewed as a paraphyletic group from which taxa like the Pogonophora , Vestimentifera (both now part of the Siboglinidae family ), Echiura and Clitellata have developed. Molecular genetic studies of Torsten H. Struck and other 2011 suggest that it is even the sipuncula only after the Polychaten family Chaetopteridae have so a very basal group of the annelids, split off. Therefore, it is to be expected that the class of the multi-bristle will be dissolved and classified as a younger synonym of Annelida. The evolutionary biological debate revolves around the question of whether the assumed common ancestor of the annelid worms, as burrowing ground dwellers without parapodia, was more like a little bristle or on the surface of the seabed corresponded to the blueprint of a polythene. In 1997, Wilfried Westheide argued that the segmental partitions were a prerequisite for the development of the lateral vessels and that the highly complex blood vessel system of many annelids can be traced back to the presence of parapodia with gills , i.e. the construction plan of the multi-bristle was the original. Torsten H. Struck confirmed this view with his investigations in 2011 and argued that the development of parapodia drove the evolution of segmentation. He summarizes the Errantia and Sedentaria , which resemble such ancestors, as a group of Pleistoannelida characterized by many plesiomorphies .

A comparatively new system in which the Polychaeta (including the Pogonophora and Vestimentifera within the Siboglinidae family) are postulated as a monophyletic group is that according to Rouse & Fauchald 1998:

Some species and genera

Phyllodoce lineata from the Belgian North Sea ,coloredwith eosin


Individual evidence

  1. ^ Wilhelm Gemoll : Greek-German school and hand dictionary . G. Freytag Verlag / Hölder-Pichler-Tempsky, Munich / Vienna 1965.
  2. Geography of Guam June 29, 2015

Web links

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