Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. B). Click on a title to look inside that book (if available): Encyclopedia of Inland Waters (2009). Phylum Annelida - Class Clitellata - Segmented Worms. Confused by a class within a class or Older systems would place the polychaetes and oligochaetes under the class Chaetopoda because both groups possess setae. Leech classification is based on the presence or absence of setae and the nature of the mouth, proboscis (feeding organ), jaws, suckers, eyes, and reproductive system. The Animal Diversity Web (online). Oligochaete classification relies largely on internal structures, especially the arrangement and number of gonads, the position of the gonoducts, and particularly the location of the male pore. The classification system given above lists 23 orders (Archiannelida was considered as one order in the classification above, while other schemes divide the group into four orders). Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. The Branchiobdellida are considered an order of Hirudinea, but they have been considered as a separate class in the past or as an order of Oligochaeta. Annelid - Annelid - Classification: Classification of free-living and sedentary polychaetes relies almost exclusively on external characters, such as the shape of the head, and on the number and nature of structures, such as appendages (including anal ones), parapodia, and setae, and on tube construction. B). Accessed at https://animaldiversity.org. Distinguishing characteristics - A clitellum is present (Fig. © 2020 Regents of the University of Michigan. E). The Animal Diversity Web team is excited to announce ADW Pocket Guides! ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. The families of leeches, organized into the four orders outlined above, are generally accepted. The latter – though without merging the Oligochaeta and Clitellata – has been proposed time and again in the past, most prominently for the distinct Moniligastrina . Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students.ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Body wall is soft and muscular (Fig. E). To cite this page: Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. B). D) or bundles of bristles on the body segments (Fig. Please see our brief essay. D) or bundles of bristles on the body segments (Fig. The following classification incorporates the views of several authorities. an order within an order? Orders were frequently ignored in the past, especially with the polychaetes, but authors have come to greater agreement as to the placement of families within orders. Setal characteristics are generally uniform among species. Disclaimer: Thus, the Haplotaxida might eventually be up-ranked to subclass status within the Clitellata or an expanded Oligochaeta, with the present suborders advancing to order rank. C). Other systems would join the oligochaetes and leeches in a single class, called the Clitellata, because both groups possess a clitellum. This class includes three main groups, the leeches (Hirudinea), the aquatic earthworms (Oligochaeta) and the branchiobdellids. This material is based upon work supported by the The ADW Team gratefully acknowledges their support. 2020. The Archiannelida and Myzostomida treated as polychaete orders in the classification system above have been considered as separate classes in the past. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services. Phylum Annelida - Class Clitellata - Segmented Worms Distinguishing characteristics - A clitellum is present (Fig. C). There are approximately 43 families in the class. B). Search in featureTaxon InformationContributor GalleriesTopicsClassification. Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control. Classification of free-living and sedentary polychaetes relies almost exclusively on external characters, such as the shape of the head, and on the number and nature of structures, such as appendages (including anal ones), parapodia, and setae, and on tube construction. Help us improve the site by taking our survey. Most authors accept the annelids as having three major classes: Polychaeta, Oligochaeta, and Hirudinea. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Wormlike body is segmented (Fig. Wormlike body is segmented (Fig. Placement of annelids within orders has been difficult because of the tremendous diversity in structure and specialization in habitat, especially in the polychaetes. May feature one or two suckers (Fig. The oligochaetes are divided into three orders based especially on the placement of the male gonopores. There are approximately 87 known families of polychaetes. The Animal Diversity Web is an educational resource written largely by and for college students. 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. Unlike the class of Polychaeta, they do not have parapodia and their heads are less developed. While some small segmented worms of the phylum. Notes - All of the annelids we find in North Dakota rivers and streams belong to the class Clitellata. This arrangement, while convenient, is not based on morphology and is not generally used. National Science Foundation Body wall is soft and muscular (Fig. May feature one or two suckers (Fig. Disclaimer: ITIS taxonomy is based on the latest scientific consensus available, and is provided as a general reference source for interested parties. Depending upon the author, annelids could consist of as many as six classes. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. However, it is not a legal authority for statutory or regulatory purposes. The bristles may be extremely small. The class Polychaeta has also been divided into subclasses or orders, the Errantiata (free-moving forms) and Sedentaria (sedentary, or tube-dwelling, forms), based on the mode of living. The clitellates comprise around 8,000 species. The bristles may be extremely small.

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