Secernentea Explained

Secernentea was a class of nematodes in the Classical Phylogeny System (Chitwood, 1958) and is no longer in use.^{[1] [2]} This morphological-based classification system has been replaced by the Modern Phylogeny system, where taxonomy assignment is based on small subunit ribosomal DNA (SSU rDNA).^{[3] [4]}

Characteristics of Secernentea are:

• Amphid apertures are pore/slit-like
• Derids are present in some; located near nerve ring
• Phasmids are present; posterior
• Excretory system is tubular
• Cuticle is striated in two to four layers; lateral field is present
• Three esophageal glands; esophageal structure varies
• Males generally have one testis
• Caudal alae are common
• Sensory papillae are cephalic only; may be caudal papillae in males
• Mostly terrestrial
• Rarely found in fresh or marine water

Systematics

See also: List of nematode families. Subclasses and orders of Secernentea are:^[5]

• Subclass Rhabditia (paraphyletic?)
  • Rhabditida
  • Strongylida
• Subclass Spiruria
  • Ascaridida^[6]
  • Camallanida (sometimes included in Spirurida)
  • Drilonematida (sometimes included in Spirurida)
  • Oxyurida (= Rhabdiasida)
  • Rhigonematida (formerly in Tylenchia)
  • Spirurida
• Subclass Diplogasteria (may belong in Rhabditia)
  • Diplogasterida
• Subclass Tylenchia (may belong in Rhabditia)
  • Aphelenchida
  • Tylenchida

Some families traditionally considered to be Rhabditida seem to be closer to the Tylenchida. If the Tylenchia are to be maintained as separate, they probably will be included therein.

Notes and References

1. Web site: WoRMS - World Register of Marine Species - Secernentea. May 24, 2018.
2. Olsen, Oliver Wilford. 1986. Animal Parasites: Their Life Cycles and Ecology. Courier Corporation. 10.1086/408868.
3. De Ley, P., and M. Blaxter. 2004. "A New System for Nematoda: Combining Morphological Characters with Molecular Trees, and Translating Clades into Ranks and Taxa." Nematology Monographs and Perspectives 2. Brill, Netherlands: 633–53.
4. De Ley, P., Wilfrida Decraemer, and A. Eyualem. 2006 "Introduction: Summary of Present Knowledge and Research Addressing the Ecology and Taxonomy of Freshwater Nematodes." CABI.
5. [Tree of Life Web Project]
6. Nickle, W.R. (ed.), (1991). Manual of Agricultural Nematology. New York, NY: Marcel Decker.