Prostomium
The prostomium ( ancient Greek πρό pró 'before' and στόμα stóma 'mouth'), also called acron or head lobe , is the name given to the tip of the annelid worms . In crustaceans and other arthropods also the name is Acron for the body tip in use, since you both taxa classic and arthropods summarized and Prostomium and Acron for homologous held.
The body of the annelid worms is predominantly made up of segments of the same type in the basic construction plan (the name-giving "annulus" of the "annulus" worms). However, this does not apply to the front and rear of the animal, which are not segmental. The presegmental region is formed from the front body sections of the typical larval form of the annelids, the trochophora . It consists of two sections. The front end that surrounds the mouth opening, the episphere, becomes the prostomium of the adult or adult animal, the buccal region behind it with the lash line (prototroch) forms the second, likewise non-segmental section, called the peristomium . The body segments arise in a segment formation zone immediately in front of the, likewise non-segmental, rear end of the body, the pygidium , whose equivalent in arthropods is called the telson .
The Prostomium the annelids is in many annelids, so almost all Wenigborstern or Oligochaeta often just an unassuming, rag-like notes before the first segment (the first "Ring"), which often obscures the mouth and in food intake as a kind of lip can be used . Many Vielborstern (Polychaeta) Prostomium and Peristomium form but a clearly recognizable head region ( cephalization ). The prostomium contains the front part of the brain and, in many species, sensory organs such as eyes , chemoreceptors , antennae and other tactile organs . The shape of the prostomium is varied in many ways, it can be hemispherical, conical, T-shaped, sometimes it is changed to elliptical, backward-protruding lobes or to a ring of cirrus or tentacles surrounding the mouth opening and then hardly as independent Body section recognizable. In some groups it is apparently divided into two by a cross seam. The prostomium can be fused with the peristomium. Often, however, a peristomium is switched on as a separate, independent body section between the prostomium and the first real segment.
Annular worms that have eyes or antennae are always localized on the prostomium; depending on the group, there are different numbers, up to three, of antennae. The cirrus and palps surrounding the mouth opening can sit on both the prostomium and the peristomium. In some groups of polychaetes, the first, or the first, body segments are also designed differently than the following and have appendages that are used for food intake.
Individual evidence
- ↑ Achim Paululat, Günter Purschke: Dictionary of Zoology. Spektrum Akademischer Verlag, 2011, p. 388.
- ↑ Volker Storch, Ulrich Welsch: Kükenthal - zoological internship. Spektrum Akademischer Verlag, 2009, ISBN 978-3-8274-1998-9 , p. 210.
- ^ A b c Gregory Rouse, Fredrik Pleijel: Polychaetes. Oxford University Press, 2001. ISBN 978-0-19-850608-9
- ↑ Zoology. Addison-Wesley Verlag, 2008, ISBN 978-3-8273-7265-9 , pp. 547, 551.