Branchiobdellae Hirudinea "Oligochaeta" (paraphyletic) and see text
1 Characteristics 2 Distribution and habitat 3 Reproduction 4 Systematics 5 Footnotes 6 References 7 External links
Clitellate annelids are segmented worms characterised by the clitellum
or girdle which is located near the head end of mature individuals.
The mouth is on the ventral surface and is overhung by the prostomium
(proboscis). The brain is not located in the head but in one of the
body segments. The clitellum is formed by a modification of several
segments, and either includes the female gonopores or is located just
behind them. During copulation, this glandular tissue secretes mucus
that keeps the paired individuals together while they exchange sperm.
Afterwards it secretes material that forms a cocoon that encircles the
animal's body and encloses the eggs and sperm. The animal works this
cocoon forward and over its head end, whereupon the ends of the cocoon
become sealed, with fertilisation and development taking place
Earthworms and their kin, in the subclass Oligochaeta, lack eyes but
have photoreceptor cells in the skin, especially in the dorsal portion
of the anterior end. They also lack parapodia and appendages on the
prostomium, the body and the periproct (terminal segment on which the
anus is located). The gonads are located in a few segments near the
clitellum, with the testes being anterior to the ovaries. There are
four bundles of one to twenty-five chaetae on each segment; these have
muscles attached to their bases and can be extended or retracted.
Leeches and their relatives, in the subclass Hirudinea, mostly have
flattened bodies, usually tapered at both ends. They have a fixed
number of segments, 33, but the segmentation is not visible externally
because the cuticle is marked with annulations. Leeches do not bear
chetae. The front few segments or head have been modified into a
sucker that usually surrounds the mouth. These segments usually bear
several ocelli on the upper side. The clitellum occupies segments 9 to
11 but is only noticeable during breeding periods. The hindermost
segments form another, larger, disc-shaped sucker located on the
underside of the body. The anus is on the dorsal surface just in front
of the posterior sucker. The body wall includes strong transverse,
longitudinal and diagonal muscles which give the animal great
flexibility and extensibility.
Distribution and habitat
Clitellates live on land, in freshwater or in the ocean. The subclass
The Acanthobdellidea, a sister group to Hirudinea, are sometimes moved
out of the
^ Manum, S. B.; Bose, M. N.; Sawyer, R. Y. T. (1991). "Clitellate
cocoons in freshwater deposits since the Triassic". Zoologica Scripta.
20 (4): 347. doi:10.1111/j.1463-6409.1991.tb00300.x.
^ a b c d e Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D.
(2004). Invertebrate Zoology, 7th edition. Cengage Learning.
pp. 459–482. ISBN 978-81-315-0104-7.
Erséus, Christer; Wetzel, Mark J. & Gustavsson, Lena (2008): ICZN rules – a farewell to Tubificidae (Annelida, Clitellata). Zootaxa 1744: 66–68. PDF fulltext Reichardt, Anna Katharina (2006): Systematische Zoologie.
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Brief description A Series of Searchable Texts on Earthworm Biodiversity, Ecology and Systematics from Various Regions of the World
Wd: Q839350 ADW: Clitellata EoL: 37 GBIF: 255 ITIS: 568832 NCBI: