Panagrellus pycnus




Rev 11/29/2022

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Morphology and Anatomy Life Cycle

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Panagrellus pycnus Thorne, 1938

Type species of the genus

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Morphology and Anatomy:



  • Monodelphic-prodelphic. Ovary  very long, lacking flexure, with  oocytes   in  several  rows  distally and a single row proximally.  

  • Oviduct short, slightly longer than the body diameter, with a scarcely discernible spermatheca at its proximal part.

  • Uterus very long, 6.8-10.9 times as long as body diameter, tubular, with eggs in different stages of development.

  • Post-vulval uterine sac well developed, 2.6-3.8  times  as  long  as  the  body  diameter,  with  very  thin  walls, 

  • Vagina  extending  inwards  to  31-43%  of  body  diameter,  sigmoid. 

  • Vulva  slightly  protruding.  

  • Rectum  short,  0.9-–1.3  times  the  anal  body  width;  three small gland-like cells are distinguishable around the  intestine-rectum  junction.

  • Tail  conical-elongate  with acute terminus; phasmids located at 34–40% of tail length from anus.


  • Reproductive  system  monorchic,  with  testis  reflexed  ventrad  anteriorly. 
  • Spicules  paired  and  symmetrical:  manubrium   ventrally   bent,   angular   hook-shaped, .
  • Gubernaculum well developed, slightly curved, about 0.4  times  spicules  length, .
  • Three small gland-like cells at beginning  of  the  cloaca. 
  • Tail  conical,  slightly  curved ventrad, conoid anterior to phasmid and them filiform. 
  • Genital  papillae  seven  pairs,  three  pre-cloacal   and four post-cloacal:  One mid-ventral adcloacal papilla
  • Phasmids at 32 to 50% of tail length

Ref: Abolafia and Vecchi, 2021

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:


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Bacteria, and diatoms (based on diatom frustules observed in intestine).

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Biology and Ecology:



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Life Cycle:

Pronanly sexually reproducing based on sperm in spermatheca and frequency of males.

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters
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Ecosystem Functions and Services:



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Abolafia, J. and Vecchi, M. 2021. Redescription and phylogenetic analysis of the type species of the genus Panagrellus Thorne, 1938 (Rhabditida, Panagrolaimidae), P. pycnus Thorne, 1938, including the first SEM study. Journal of Nematology, 53:1-20.

Hechler, H.C. 1971. Taxonomic Notes on Four Species of Panagrellus Thorne (Nematoda: Cephalobidae). 3:227-237.

Thorne,  G.  1939.  Notes  on  free-living  and  plant-parasitic  nematodes.  V.  Proceedings  of  the  Helminthological Society of Washington 6:30-32.


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Copyright © 1999 by Howard Ferris.
Revised: November 29, 2022 .