Diagnosis (modified from Fonseca & Decraemer 2008)
Short body length (< 0.8 mm). Small somatic setae often present. Six outer labial and four cephalic sensillae usually setiform. Buccal cavity tubiform, funnel-shaped or conoid, often with cuticularised walls; denticles usually present, but difficult to observe in small species. Circular amphideal fovea usually 1.5–2.0 or more head diameters from anterior end. Posterior part of pharynx enlarged forming a single or double bulb without valves. Secretory-excretory system usually absent. Female reproductive system short to medium sized; vulva near mid-body. Spicules mostly arcuate and short (<2 abd). Tail usually with ventrally curved conical anterior portion and dorsally curved cylindrical filiform posterior portion. Spinneret a long and slender cone or cylinder.
*Dorso–caudal apophyses present but very thin and may be difficult to observe. **From re–description by Jensen (1992)
The taxonomy of all marine Monhystrella species was revised by Fonseca & Decraemer (2008), who provided a detailed diagnosis of the genus and a key to all thirteen valid marine species; no new marine species have been described since.