Xyalidae. Body very small (about 0.5 mm or less) and slender. Cuticle distinctly annulated or smooth, without lateral differentiation. Cephalic crown composed of ten (6 + 4) smooth setae, without additional setae. There may be scarce cervical and somatic setae along the body. Amphid large, round or slightly longitudinally oval. Esophastoma elongate conical to near cylindroid, with sclerotised rhabdions, surrounded with esophageal cuff. Esophagus slightly widening posteriad, without a terminal bulb. Renette cell not known. Prodelphic female gonad supplied with a postvulvar sac and to the left of midgut. Male gonads either paired (anterior outstretched testis to the left and posterior reflected testis to the right of midgut) or single anterior outstretched testis to the left of midgut. Spicules small, slightly bent, distally fused in one species (A. unita). Gubernaculum with small dorsocaudal apophysis or absent. Tail consists of proximal conical and distal cylindrical portions ending with terminal dropshaped widening.
Type species: Amphimonhystrella megastoma Timm 1961.