Nematode of the Week

Mononchus truncatus

Photo Gallery
Mononchus truncatus Bastian, 1865

This week's featured nematode was recovered from the jumbo valley fen (map) located in the sandhills region of Nebraska. Fens are a rare type of wetland found in the sandhill wetlands. The sandhill wetlands are formed in depressions in sandhills areas where the groundwater intercepts the land's surface. The area is the largest contiguous tract of grassland remaining in the U.S. and also the largest stabilized sand dune area in the Western Hemisphere. The Sandhills encompass more than 19,000 square miles and overlie several groundwater aquifers of the Ogallala Formation. More than a million acres of lakes, marshes and wet meadows are present in the Sandhills.  This Mononchus truncatus female was recoved from a soil wash taken from the first 18 cm of a 2 m core sample. Other predacious nematodes from this fen include: Ironus sp., Tripyla sp., and Prionchulus sp.

Habitat: We have recoved this nematode from Nebraska (fens, corn and soybean fields), Kansas (tallgrass prairie) and Manitoba (bogs).

Allen Szalanski


Descriptions
  • Cobb (1917)

    • M. truncatus Bastian.  Esophagus conoid, its lining well developed.  Intestine about 12 cells in girth, more or less distinctly tessellated. Lateral fields broad and distinct.  It is a question whether to retain this species on the basis of Bastian's original description, or to accept Biltschli's description as a rehabilitation of Bastian's species.  It is hardly likely that any species of Mononchus is destitute of labial papillae, and in this respect Bastian's description seems defective. The extreme reduction of the labial papillae so far recorded is shown in megalaimus.  Butschli and later authors describe and figure the papillae of truncatus as setose.  It seems hardly likely that Bastian would have overlooked setose papillae such as those figured by Butschli.  In that case Bastian's truncatus should be retained as a species, probably having very inconspicuous labial papillae similar to those of megalaimus, while the data given by Butschli may be taken as establishing a new species, for which the name obtusus is proposed. 
    Found in a small pool, among decaying moss and liverwort, England. 
  • Jensen and Mulvey (1968)

    • Mononchus truncatus Bastian, 1865

    DIMENSIONS OF OREGON SPECIMENS
    Five females.  L. @ 1.64 mm (1.48 - 1.92); A = 37 (31 - 44); B 5.7 (5.5 - 6.5); C = 6 (5.0 - 6.4); V = 50% (47 - 52); buccal cavity; 15 x 38 u (14 - 16 x 34 - 41); tail length = 0.27 mm (0.20 - 0.30); egg = 40 x 82 u.
    Female.  Body assumes a straight position, except for the arcuate tafl region, when relaxed by heat; with truncate anterior termini and elongate-cylindroid posterior termini.  Labial region continuous with body contour with lips almost obscure.  Buccal cavity thin-walled, elliptical, about two and one-fourth times as long as wide, bearing medium-sized dorsal tooth at upper third of cavity.  Amphid apertures about one third of corresponding cavity width near level of dorsal tooth.  Transverse ridges, probably sutures, opposite dorsal tooth.  Didelphic; may be hermaphroditic, as structures resembling spermagonia occur in uteri.  Tail elongate-conoid, then cylindrical with caudal glands and terminal spinneret, and usually with one or two short setae at terminus.  Four pair of caudal pores usually occur in the following areas: two median pairs in the anterior fourth of tail, a dorsal pair at anterior third, and a ventral pair in posterior third of tail.
    Habitat.  A common inhabitant of Oregon soils where it occurs in cultivated areas, although uncultivated stream banks and ocean shore sites seem to be preferred.

References:
  • Jensen, H.J. and R.H. Mulvey. 1968. Predaceous Nematodes (Mononchidae) of Oregon. Oregon State University Press: Corvallis. 
  • Cobb, N.A. 1917. The Mononchs (Mononchus Bastian, 1866). A genus of free-living predatory nematodes. Soil Science 3: 431-486.