Secernentea

Secernentea
Scientific classification
Kingdom:	Animalia
Phylum:	Nematoda
Class:	Secernentea
Subclasses
Diplogasteria (disputed) Rhabditia (paraphyletic?) Spiruria Tylenchia (disputed) and see text

Secernentea was a class of nematodes in the Classical Phylogeny System (Chitwood, 1958) and is no longer in use [2, 3]. This morphological-based classification system has been replaced by the Modern Phylogeny system, where taxonomy assignment is based on small subunit ribosomal DNA (SSU rDNA) [4, 5].

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

Subclasses and orders of Secernentea are:^[1]

• Subclass Rhabditia (paraphyletic?)
  • Rhabditida
  • Strongylida
• Subclass Spiruria
  • Ascaridida
  • 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.

References

Wikimedia Commons has media related to Secernentea.

2. “WoRMS - World Register of Marine Species - Secernentea.” n.d. Accessed May 24, 2018. http://www.marinespecies.org/aphia.php?p=taxdetails&id=2133.

3. Olsen, Oliver Wilford. 1986. Animal Parasites: Their Life Cycles and Ecology. Courier Corporation. doi.org/10.1086/408868

4. 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.

5. 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.