Geocenamus   

  

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Rev 11/21/2019

  Classification Hosts
Morphology and Anatomy Life Cycle

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Classification:

Rhabditida
       Tylenchina
        Tylenchoidea
             Merliniidae
             Merliniinae

             Geocenamus Thorne & Malek, 1968

    Synonyms:
      Hexadorus (Ivanova & Shagalina, 1983)

As of October 2003, the Zoological Record indicates 51 species names associated with this genus.

The genus Geocenamus was established by Thorne and Malek (1968) in the subfamily Tylenchoryhynchinae. The name of the genus is derived from a contraction of Geographic center of North America, reflecting the region from which it was first described.

The genus is distinguished from other genera within the subfamily by a labial disc. The cephalic framework is weak and the stylet slender.

Currently (2005) , Geocenamus contains 14 species. 

Ref. Chitambar and Ferris, 2005.

 

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Morphology and Anatomy:

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 Geocenamus can be differentiated from Merlinius mainly by the derived characters: bulbous labial region, an elongate stylet with a conus distinctly longer than the shaft, and a distinctly round to hexagonal labial disc. 

Body medium-sized.  

Labial region bulbous.  SEM face view with well-marked, round labial disc.  First lip annule divided into six sectors, lateral sectors smaller.  Labial framework weakly developed.  

Lateral field with six lines.  

Deirids absent (but reported inconspicuous by Siddiqi, 1986).  

Stylet slender, 25 to 130 µm long, cone longer than shaft. 

Tail conoid to almost cylindroid.  
Male: Spicules without velum, blunt-ended.  

Gubernaculum not protruding from cloaca.

[Ref: Fortuner & Luc (1987).]

Body size range for the species of this genus in the database - Click:

Key to Species of the Genus Geocenamus

 

1.         Stylet length equal to or greater than 90 µm………………………………                2

               1a.    Stylet length 20-49 µm……………………………………………               5

               1b.    Stylet length 50-69 µm……………………………………………               8 

2(1).     Tail cylindrical, terminus broadly rounded, annulated……………                  3

   2a.    Tail conical, terminus narrowly rounded, smooth…….……………                 4

3(2).     Stylet length 120-134 µm; lateral field completely areolated

            throughout entire body; cephalic framework strongly     

            sclerotized……………………………………………            G. arealoferus

  3a.     Stylet length 96-107 µm; lateral field not areolated

throughout entire body; cephalic framework lightly

sclerotized……………………………………………            G. nurserus    

4(2a).   Lateral field incisures completely crenate;

L =1530-1813……………………………………….            G. kirjanovae

              4a.     Lateral field incisures not crenate; L = 1800-2150….    G. tokobaevi

            5(1a).   Longitudinal striae extend throughout body………..                                       6

              5a.     Longitudinal striae absent except in lateral field…...                                        7

            6(5).     Tail terminus narrowly rounded almost to a point;

                        longitudinal striae 26-28;  stylet length 28-29 µm.…                  G. patternus

              6a.     Tail terminus rounded but not narrowly to a point;

                        longitudinal striae 20; stylet length 26 µm…………                   G. squamatus

            7(5a.)   Tail terminus broadly or narrowly rounded, smooth

                        or annulated; lateral field areolated on tail,

 4 incisures posterior to phasmid, ……………….                   G. tenuidens    

                                                                                                = G. arcticus  

                                                                                                = G. uralensis    

              7a.     Tail terminus digitate, smooth; Lateral field not

areolated on tail, 6 incisures posterior to phasmid…          G. khashanicus       

            8(1b).   Longitudinal striations intersect transverse annules

                        forming series of blocks over entire body…………                G. longus

              8a.     Longitudinal striations absent outside of lateral

                        field………………………………………………..                                   9

            9(8a).   Lip region with 12 longitudinal incisures…………                 G. deserticola

              9a.     Lip region with 6 longitudinal incisures…………..                                     10

          10(9a).   Female stylet 67 µm, L = 1120 µm……..…………              G. superbus

            10a.     Female stylet 50-57 µm, L = 801-996  µm………...             G. angelescresti

 Ref: Chitambar and Ferris, 2005

 
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Distribution:

 

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Economic Importance:

D-rated pest in California Nematode Pest Rating System.

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Feeding:

 

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Hosts:

For an extensive host range list for this genus, click
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Life Cycle:

For Ecophysiological Parameters for this genus, click 
 
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Damage:

 

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Management:

 

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References:

Chitambar, J.J. and H. Ferris. 2005. Geocenamus angelescresti n. sp., a diagnostic key and compendium to the species of the genus Geocenamus Thorne and Malek, 1968 (Nematode Belonolaimidae) Journal of Nematology 37:429-437.

Fortuner & Luc, Rev. Nematol. 10(2):183-202 (1987).

 

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Copyright © 1999 by Howard Ferris.
Revised: November 21, 2019.