Worm

As worms ( singular: worm) refers to a whole series of sometimes only very distantly related invertebrates. They are characterized by an elongated, tubular body and crawling locomotion. Originally, attempts were of zoology to provide all worm-like animals because of their physical characteristics in a close family relationship and in the class of worms ( Vermes ) summarize. Because of the many different worm-like species, merely because of their different internal structure, barely related to each other ( Heterophylie ), this idea had to be abandoned. The juxtaposition of " Higher worms " ( Annelida ) and " Low worms " ( Aschelminthes and Platyhelminthes ) is now completely outdated. Nevertheless, all these animals morphologically so similar by convergent evolution, that for a more general and popular view of the term worm can still be used and will.

Features

A worm is called an animal with a stretched, rotating round or flattened body, the way radial symmetry often appears to the outside, even if the animal is in fact bilaterally symmetrical - all worms are among the Bilateria. The absence of extremities such as legs or antennae, and a resulting creeping mode of locomotion are also typical. Most worms also lacks a solid inner or outer skeleton ( exoskeleton ), often the animals by a hydraulic skeleton, which is a fluid-filled system of chambers in the interior of the body, having regard.

Erroneously, the German term worm is also used in some insect larvae, such as for the larva of the blister beetle or the mealworm, but due to several characteristics, such as the presence of legs and antennae and a chitin shell, can be clearly identified as insect and not therefore constitute a worm.

In the Middle Ages were often many other " crawling animals" referred to as worms (see dragon ).

System

All worms are among the invertebrates ( invertebrates ). Except for the acorn worms they are among the Urmundtieren ( Protostomia ). That it is not possible to make a more general classification for all types of worms, shows what are the worms for a heterogeneous group. It can be found herein both lophotrochozoans and molting animals ( Ecdysozoa ). Among the various strains of animals in which there are worms include:

• Nematodes ( Nematoda )
• Horseshoe worms ( Phoronida )
• Hedgehog worms ( Echiura )
• Calyx worms ( Entoprocta )
• Gnathostomulids ( Gnathostomulida )
• Gill hole Animals ( Hemichrodata )
• Scratch worms ( Acanthocephala )

• Arrow worms ( Chaetognatha )
• Flatworms ( Platyhelminthes )
• Priapswürmer ( Priapulida )
• Segmented worms ( Annelida )
• Hairworm ( Nematomorpha )
• Spray worms ( Sipunculida )
• Ribbon worms ( Nemertini )

Earthworms belong to the annelids.

The family of arthropods, which include insects, arachnids and crustaceans belong, to find the tongue worms ( Pentastomida ), which belong to the crustaceans (Crustacea ), as wormlike representative.

Scientists that deal with one or more of the above strains should be, ( translated as "worm watchers " ) still known as Helminthologen.

Importance

Some parasitic worms, tapeworms, roundworms and flatworms known as intestinal worms, can in humans or in other animals cause worm disease, but there are also many for humans harmless worms or even those that are useful (eg, the earthworm that the quality of the soil he inhabits, enhanced). Because of the heterogeneous origin of the various worms habitats and ways of course are just as different. Worms do not only come ashore before (like the above mentioned earthworm ), but also marin such as the beard worms that can survive even at the extreme locations of the deep sea in large numbers. Worms have in ecosystems often very important as decomposers, but are themselves often food for some carnivorous animals such as birds, small mammals or fish.