Prochaetoderma yongei is a small, slender, translucent species with flat-lying spicules oriented anterior-posterior except where they diverge along the ventral midline. Body has three distinct regions reflecting the internal anatomy: the anterium (with the oral shield), the trunk, and the posterium. Total body length averages 0.06-0.11 in (1.5-2.8 mm). Trunk diameter averages 0.01-0.02 in (0.3-0.4 mm), with greatest diameter of 0.02 in (0.6 mm). The posterium is about one-quarter the total length. An opaque, thickened patch of cuticle at the ventral junction of the trunk and posterium is characteristic of the species. Oral shield is small, and is divided into two lateral shields with indistinct spicules. The cloaca is rounded. Solid spicules are flat with the base shorter than the blade; blade is broad and triangular with median keel and sharp distal point. There is a pair of large, cutilar jaws and a small distichous radula. The central radula plate is short.
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