Belt worms
Belt worms | ||||||||||||
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Systematics | ||||||||||||
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Scientific name | ||||||||||||
Clitellata | ||||||||||||
Michaelsen , 1919 |
The belt worms (Clitellata) are a class of annelid worms . They include at least 3800 species that form a natural ( monophyletic ) unit. They include such well-known forms as earthworms or leeches.
Mark
The girdle worms are named after a structure called the clitellum . It is a region of the epidermis that forms an elevation on the body due to its numerous glands . The clitellum surrounds the body in a belt-like manner in a few segments lying one behind the other on the front half of the body. The girdle worm eggs develop in a cocoon that is secreted by the clitellum.
In contrast to the many bristles, the animals have few or no bristles, no lateral, leg-like outgrowths ( parapodia ), no antennae and no cirrus (small mobile feet).
Reproduction
The belt worms are hermaphrodites (simultaneous hermaphrodites ). The gametes (sex cells) are released into the clitellum. After fertilization, the clitellum is wiped off. The animals practice external fertilization and bury their eggs deep underground to protect them from predators.
Systematics
The belt worms are traditionally (simplified) subdivided into two taxa , whereby it should be noted, however, that the little bristle probably do not form a uniform (monophyletic) group.
- Little bristle (Oligochaeta) with about 3500 species; Occurrence mainly in fresh water, but also on land and in the sea.
- Flukes (Hirudinea) with about 300 species; Occurrence mainly in fresh water, but also on land.
Individual evidence
- ^ W. Westheide: Clitellata, belt worms. In: W. Westheide, R. Rieger: Special Zoology, Part 1: Protozoa and invertebrates. 2nd Edition. Elsevier spectrum, Munich 2007.