Phylum Nematoda  

                                          Rev 09/04/2014

Classes, Sub-classes and Orders

Modern Classification

Modern Phylogeny Menu (De Ley and Blaxter, 2002)

Nematoda
 
Enoplea Chromadorea
Enoplia Dorylaimia Chromadoria
 
  Enoplida   Dorylaimida   Rhabditida
  Triplonchida   Mermithida   Plectida
Mononchida Araeolaimida
      Dioctophymatida   Monhysterida
      Trichinellida   Desmodorida
      Isolaimida   Desmoscolecida
      Muspiceida   Chromadorida
      Marimermithida    
 
   Key to the Orders of Nematoda
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Classical Phylogeny Menu (Chitwood, 1958)

In a classical morphology-based classification system of the Nematoda there are five sub-classes and nineteen orders; those that contain plant-feeding genera are marked with an asterisk (*).

Nematoda
 
Adenophorea Chromadorea
   
Enoplia Chromadoria Rhabditia Spiruria Diplogasteria
         
  Enoplida   Araeolaimida   Rhabditida   Spirurida   Diplogasterida
  Isolaimida   Chromadorida   Strongylida   Ascarida   *Tylenchida
  Mononchida   Desmoscolecida       Camallanida    
  *Dorylaimida   Desmodorida       Drilonematida    
  Stichosomida   Monhysterida            
  *Triplonchida                

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Comparison of Morphology- and DNA-based Classifications:

Classification Based on Classical Morphology

Adenophorea Chromadorea
Enoplia Chromadoria Rhabditia Spiruria Diplogasteria
  Enoplida   Araeolaimida   Rhabditida   Spirurida   Diplogasterida
  Isolaimida   Chromadorida   Strongylida   Ascarida   *Tylenchida
  Mononchida   Desmoscolecida       Camallanida    
  *Dorylaimida   Desmodorida       Drilonematida    
  Stichosomida   Monhysterida            
  *Triplonchida                

 

Classification Based on SSU rDNA

Enoplea Chromadorea
Enoplia Dorylaimia Chromadoria
  Enoplida   Dorylaimida   Rhabditida
  Triplonchida   Mermithida   Plectida
Mononchida Araeolaimida
      Dioctophymatida   Monhysterida
Trichinellida Desmodorida
      Isolaimida   Desmoscolecida
      Muspiceida   Chromadorida
      Marimermithida    
           

 

Morphological Basis SSU rDNA Basis The classification of organisms above the genus and species levels is not governed by the International Rules of Zoological Nomenclature.  In essence, higher classification schemes represent expert opinion based on available evidence.  Several classification systems have been proposed for nematodes.  New opinions on the relationships among taxa are emerging from molecular data.  At the present time, we will use for Nemaplex a widely accepted scheme based on nematode morphological and anatomical characters.
Classes Classes
Sub-classes Sub-classes
Orders Orders
Comparison

References

Key to the Orders of Nematoda
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Other classification categories:

  1. mode of parasitism

  2. feeding habits

  3. habitats and distribution

 

Name endings of different levels of taxonomic organization:

  1. classes (ea)
  2. sub-classes (ia)
  3. orders (ida)
  4. sub-orders (ina)
  5. superfamilies (oidea)
  6. families (idae)
  7. sub-families (inae)

 

Classes

The Phylum Nematoda consists of two classes in both Classical and Modern Classification Systems:
Classical System Modern System
Class Chromadorea


1. pore-like or slit-like amphid apertures - labial.
2. deirids present in some, near nerve ring.   
3. phasmids present, generally posterior.
4. excretory system tubular.
5. cuticle 2 to 4 layers, striated; lateral field present.
6. esophagus varies but has 3 esophageal glands.   
7. male generally with 1 testis.
8. caudal alae common.
9. sensory papillae cephalic only, although may be caudal papillae in males.
10. almost exclusively terrestrial, rarely freshwater or marine.
Class Chromadorea

1. pore-like or slit-like amphid apertures vary from labial pores or slits to post-labial elaborate coils and spirals.
2. cuticle usually annulated, sometimes ornamented with projections and setae.
3. phasmids present or absent, generally posterior.
4. esophagus usually divided into bulbs, with 3 to 5 esophageal glands.   
5. excretory system glandular or tubular.
6. female with one or two ovaries.
7. caudal alae present or absent.
      
Class Adenophorea

1. amphids post-labial, variable shape, pore-like to elaborate.
2. deirids absent.
3. phasmids generally absent.
4. simple glandular, non-tubular excretory system when present.
5. male generally with 2 testes.
6. caudal alae rare.                      
7. sensory papillae both cephalic and somatic.
8. marine, freshwater, terrestrial.
Class Enoplea

1. amphids pocket like, not spiral, usually post-labial.
2. cuticle smooth or finely striated.
3. phasmids present or absent.
4. esophagus cylindrical or bottle-shaped with 3 to 5 esophageal glands, stichosome or trophosome present in some.
5. simple non-tubular excretory system, usually a single cell.
6. female generally with two ovaries.
7. male generally with two testes.
8. caudal alae rare.
     
             
 

Taxonomy and Nomenclature

Taxonomy is the systematic grouping of organisms according to their natural relationships. While based on thorough investigation of organism features and structures, opinions may differ among experts regarding the importance and significance of individual features as indicators of relationship.  Additionally, new technologies are developed, for example the transmission and scanning electron microscopes, biochemical and molecular techniques, which allow new interpretations of the relationships.  Consequently, although guided by the International Rules of Zoological Nomenclature, the taxonomy of nematodes is seldom static. A case in point is the evolution of genus and species names in the genera Meloidogyne and Criconemoides.

Changes in taxonomy are, of course, important indicators of the evolution of our understanding of the organisms.  However, they can give rise to confusion, particularly among those not at the center of the debate.  This is not a new problem; Christie (1959) drew attention to the issue in the preface of his book "Plant Nematodes: Their Bionomics and Control":

            “Somewhat ironically, but quite understandably, common names can lend stability to nomenclature, at least in nematology, and thereby help avoid confusion. Not being subject to rules (let us hope they never will be), common names can remain the same regardless of how many times scientific names are changed.  What we have been calling Hoplolaimus coronatus can still remain the crown-headed lance nematode even though we must now call it (at least temporarily) Hoplolaimus tylenchiformis.  The economic nematologist, if desirous of smoothing the way for the extension service, may do well to bear this point in mind.  A county agent who works with growers of ornamentals and has had occasion to learn that Rotylenchus buxopholus is a parasite on boxwood roots, may be excused for a moment of confusion when he first encounters the name Gottholdsteineria buxophila.”


References:

Christie, J.R. 1959. Plant Nematodes: Their Bionomics and Control. Univ. Florida Agric. Expt. Sta. 256p.

De Ley, P. and Blaxter. M. 2002.  Systematic position and phylogeny.  In:  D. L. Lee (ed) The Biology of Nematodes.

De Ley, P. and Blaxter. M. 2004.  A new system for Nematoda: combining morphological characters with molecular trees, and translating clades into ranks and taxa.  Nematology Monographs and Perspectives, 2004: 633-653.

De Ley, P., Decraemer, W. & Eyualem-Abebe. (2006). Introduction, summary of present knowledge and research addressing the ecology and taxonomy of freshwater nematodes. Pp 3-30 in Eyualem-Abebe, Andrássy, I. & Traunspurger, W. (Eds). Freshwater Nematodes, Ecology and Taxonomy. CABI Publishing, Wallingford, UK.

Decraemer, W. 2011.  Stsyematics and molecular phylogenetics.  Part I.  General systematics.  University of Ghent, 89p.

Maggenti, A.R. 1981.  General Nematology.  Springer Verlag, New York.

 

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