Paratylenchus (Gracilacus) latescens
 (Raski, 1976) Siddiqi, 1986
Tylenchulidae: Paratylenchinae
Photo Gallery- Konza Prairie

Description (from Raski, D.J. 1976.  Revision of the genus Paratylenchus Micoletzky, 1922 and descriptions of new
      species.  Part III of three parts - Gracilacus.  J. Nematol. 8: 97-115):
Paratypes (19 slender females): L = 0.27 (0.22-0.29) mm; a = 19 (14-23); b = 2.2 (1.7-2.5); c = 13 (10-13); V =
        16 (14-18) 71 (68-73); stylet = 75 (63-80) mm; prorhabdion = 67 (58-740 mm; excretory pore = 71 (64-82) mm.
Holotype (female): L = 0.25 mm; a = 17; b = 2.3; c = 10; V = 17 72; stylet = 71 mm; prorhabdion = 63 mm; excretory pore
      = 74 mm.
Paratypes (8 males): L = 0.29 (0.25-0.35) mm; a = 26 (20-29); b = 3.5 (3.3-3.7); c = 12 (11-13); spicules = 20 (18-23)
      mm; gubernaculum = 4 mm; T = 37 (27-47); excretory pore = 65 (58-77) mm.
Allotype (male):  L = 0.35 mm; a = 29; b = 3.6; c = 13; spicules = 23 mm; gubernaculum = 4 mm; T = 47; excretory pore =
      77 mm.
Paratypes (5 swollen females): L = 0.37 (0.36-0.39) mm; a = 5.5 (4.1-9.3); b = 3.8 (3.6-4.1); V = 78-79 [see drawing,
     fig. 5-6]; excretory pore = 111 mm.

     Female: Body almost straight, only slightly curved ventrad after fixation.  Head rounded; submedian lobes or lips only slightly distinguished on anterior surface.  Head sclerotization light; stylet guiding apparatus appears as two darker, almost straight lines near base of sclerotization.  Stylet slender; slightly curved ventrad; knobs moderately developed, backwardly directed.  Length of stylet shaft, plus knobs 8 mm [7 (5-10) mm in paratypes].  Excretory pore near base of stylet [see drawing, fig. 1].  Hemizonid small; immediately posterior to excretory pore.  Valve in metacorpus 9 micrometers long.  Isthmus distinct, slender, 11 mm long, 2 mm wide.  Esophago-intestinal valve small, lobate.  Ovary outstretched; spermatheca elongate, about twice as long as wide; filled with sperm [see drawing, fig. 2].  Vulva lips rounded; protrude slightly, lateral vulvar membranes lacking.  Tail broadly conoid; tapers only slightly to bluntly rounded terminus.  Average width of body annules ranges from 1.0-1.4 mm (1.0-1.6 in paratypes).  Lateral field with 3 incisures equally spaced; inner incisure lighter than outer 2 [see drawing, fig 3].
     Swollen female:  Body variously swollen; greatly variable in size [see drawing, fig. 5-6]; often reniform with distinctly projecting tail.  Head rounded.  Stylet of fully swollen females invariably broken in collection process.  Metacorpus greatly enlarged, 20-28 mm in width; swells gradually but major swelling 30-35 mm long.  Isthmus remains slender but posterior bulb enlarges slightly to 9-10 mm wide by 11-13 mm long.  Ovary coils many times; few eggs seen are oval, nearly spherical and occur singly in uterus.  Body narrows abruptly immediately posterior to vulva; then becomes broadly conoid; tapers slowly to blunt rounded terminus.  Cuticle very thick, with annules coarse, especially in head region.  Lateral field indistinct in most swollen females; seen as 3 incisures in a few.  Tail elongate and terminus bluntly rounded.  Swollen females found completely inside root tissues of host plant.
    Male: Body curves slightly ventrad after fixation.  Head rounded; sclerotization light [see drawing, fig. 7].  Stylet lacking; esophagus degenerate.  Hemizonid immediately posterior to excretory pore.  Testis outstretched, with large, irregularly-shaped cells in anterior half; filled with numerous smaller sperm in posterior half [see drawing, fig. 8].  Testicular gland distinct (40-49 mm in paratypes).  Spicules curve very slightly ventrad.  Cloacal sheath short, without projecting posterior margin.  Indistinct caudal alae extend about 8-9 mm anterior and posterior to cloacal opening.  Tail broadly conoid; annules distinct almost to bluntly rounded terminus.  Average width of body annules ranges from 1.0-1.4 mm.  Lateral field with 3 incisures as in female.
      This species is most closely related to G. aculenta from which it differs in longer stylet [58 (51-66) mm for G. aculenta] and length of esophagus (b = 2.4-4.1 in G. aculenta).
     Type host:  mesquite, Prosopis sp.
     Type locality: Weslaco, Texas.
     Distribution:  9 females, 3 males and 2 juveniles found in soil about roots of Mesembryanthemum sp. at Dillon Beach, Marin County, California; 7 females, 2 males and 3 juveniles from soil about strawberry, Noyo, Mendocino County, California.
     Notes: Determined by Peter Mullin.  G. latescens is apparently rare in prairie soils (we've only seen 7 slender females out of over 4000 nematodes examined; no males or juveniles of sthis species have been observed); this may be due in part to its endoparasitic feeding habit later in life.  We have also recovered one specimen of G. aculenta (i.d. based primarily on stylet length and b ratio) from our Konza samples.  In addition, specimens of an undetermined Gracilacus species have been recovered from 9 Mile Prairie near Lincoln, Nebraska, which are similar to G. latescens, except that the slender females appear to uniformly retain the fourth-stage juvenile cuticle and the stylet, while very degenerate, remains visible in the males.

Comparison between G. latescens paratypes and specimens from Konza Prairie:

Konza Specimens:
L (mm):
Stylet (mm):

         Raski, D.J. 1976.  Revision of the genus Paratylenchus Micoletzky, 1922 and descriptions of new species.  Part III of
               three parts - Gracilacus.  J. Nematol. 8: 97-115.
         Raski, D.J.  1991.  Tylenchulidae in agricultural soils.  Chapter 17, pp. 761-794 in: Manual of Agricultural
       Nematology, W.R. Nickle, ed.  Marcel Dekker, Inc., New York.
         Siddiqi, M.R.  1986.  Tylenchida: Parasites of Plants and Insects.  Commonwealth Agricultural Bureaux, Slough, UK.
               645 pp.
 The most notable features of this nematode are its small size (260 - 288 mm in our specimens, with an average of 270 mm) and its extremely long stylet (64.8 - 71.2 mm, average 68.6 mm).  As part of a survey of nematodes associated with various tallgrass prairie plants, we've found G. latescens associated with roots of several grasses, including big bluestem, little bluestem, Scribner's panicum, and bluegrass. In this species, as in at least some other species of Gracilacus, the mature females are sessile endoparasites and as they feed, become large and swollen with age.  Since we have not yet dissected any roort tissue (focusing on soil extracts), we have not recovered any such swollen forms from our samples.

-Peter Mullin

This species included in the Criconematid Project

DNA Sequences Obtained
Specimen: Collected:
KonzaI AC-89 Konza Prairie, First survey