World Library  
Flag as Inappropriate
Email this Article

Clitellata

Article Id: WHEBN0003653061
Reproduction Date:

Title: Clitellata  
Author: World Heritage Encyclopedia
Language: English
Subject: Leech, Haplotaxida, Almidae, Ainudrilus geminus, Bathydrilus vetustus
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Clitellata

Clitellata
Temporal range: Triassic–Recent[1]
Є
O
S
D
C
P
T
J
K
Pg
N
Earthworm
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Subclasses

Branchiobdellae
Hirudinea
"Oligochaeta" (paraphyletic)
and see text

The Clitellata are a class (biology) 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, they do not have parapodia and their heads are less developed.

Contents

  • Habitats 1
  • Reproduction 2
  • Systematics 3
  • Footnotes 4
  • References 5
  • External links 6

Habitats

Most clitellates live on land, in freshwater or in the ocean.

Reproduction

All clitellata are hermaphrodites. During reproduction, the clitellum secretes a coat which hardens. The worm then creeps out backward from the coat and deposits either fertilized zygotes or both ovae and sperm into the coat, which is then packed into a cocoon. The zygotes then develop directly in the cocoon without passing through a larval stage (as opposed to other annelids, e.g. Polychaeta.) This mechanism is considered to be apomorphic (a newly derived characteristic rather than an evolutionarily ancestral one).[2]

Systematics

According to modern phylogenetic analyses, the Clitellata are considered to be a monophyletic subclade of the polychaetes.

Historically, the group was classified into the subclasses Oligochaeta and the Hirudinea. The oligochaetes contained the tubificids (Naididae, Lumbricidae, and Lumbriculidae - commonly the tube worms and the earthworms. The Hirudinea contained the leeches and the branchiobdellids. Modern analysis has revealed Branchiobdella and Hirudinea are two sister groups to the lumbriculids and they are daughter groups to the tree of oligochaetes. Hence, the terms Oligochaeta and Clitellata are considered synonymous.

The Acanthobdellidea, a sister group to Hirudinea, are sometimes moved out of the Hirudinea as a distinct subclass, too. Overall, clitellate phylogeny is not well resolved.

Namely, the Acanthobdellidea, Branchiobdella and Hirudinea are monophyletic, but actually are embedded among the Oligochaeta, which are actually an evolutionary grade of lineages that are outwardly similar, but not actually very close relatives. In particular, the leeches and earthworms appear to be very close relatives. Two approaches are possible:[3]

  • abolish Oligochaeta as traditionally delimited in favor of a number of smaller monophyletic lineages
  • treat Oligochaeta and Clitellata as synonymous while splitting up the traditional "oligochaetes" into monophyletic lineages.

Footnotes

  1. ^ Manum, S. B.; Bose, M. N.; Sawyer, R. Y. T. (1991). "Clitellate cocoons in freshwater deposits since the Triassic". Zoologica Scripta 20 (4): 347.  
  2. ^ Reichardt (2006): pp.63, 67-68
  3. ^ Erséus et al. (2008)

References

  • 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.

External links

  • Brief description
  • A Series of Searchable Texts on Earthworm Biodiversity, Ecology and Systematics from Various Regions of the World
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.