The clitellum is a thickened
glandular and non-segmented section of the body wall near the head in
earthworm
An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...
s and
leeches
Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bo ...
, that secretes a
viscid sac in which eggs are stored.
It is located near the anterior end of the body, between the fourteenth and seventeenth segments. The number of the segments to where the clitellum begins and the number of segments that make up the clitellum are important for identifying earthworms.
In
microdrile
Microdriles (small worms Worms may refer to:
*Worm, an invertebrate animal with a tube-like body and no limbs
Places
*Worms, Germany
Worms () is a city in Rhineland-Palatinate, Germany, situated on the Upper Rhine about south-southwest of ...
earthworms, the clitellum has only one layer, resulting in a smaller quantity of eggs than that of the
megadrile
A megadrile is a kind of worm, a mostly terrestrial oligochaete. Megadriles are placed within the superorder Megadrilacea, and include Moniligastrida and Lumbricina (or the order Haplotaxida
The Haplotaxida are one of two orders within the ann ...
earthworms, which have larger multi-layered clitellum that have special cells that secrete
albumin
Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...
into the worms' egg sac.
The clitellum is part of the reproductive system of
clitellate
The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycles. The clitellates comprise around 8,000 species. Unlike the class of Polychaeta, th ...
s, a subgroup of
annelid
The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
s which contains
oligochaetes
Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms ...
(earthworms) and hirudineans (leeches). The clitellum is a thick, saddle-like ring found in the epidermis (skin) of the worm, usually with a light-colored pigment. To form a cocoon for its eggs, the clitellum secretes a
viscous
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
fluid.
This organ is used in sexual reproduction of some annelids, such as leeches.
In earthworms, the clitellum can only be seen when the worm is sexually mature. It may be white, orange-red or reddish-brown in colour. Earthworms are ready to mate when their clitellum is orange.
In leeches, the clitellum appears during mating season, where it is used for both sexual reproduction and the secretion of a cocoon for the eggs.
[ ] Its color is usually slightly lighter than that of the body of the annelid. Occasionally, living segments of the worm will be shed with the clitellum.
See also
*
Earthworm reproduction
References
Further reading
*
*
*
Annelid anatomy
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