Mizelleus wallagonius is a small, elongated fluke with a bilobed head featuring three pairs of head organs, with the posterior pair being bilobed and connected by fine ducts. It has two pairs of eyespots, with the posterior pair slightly larger. The pharynx is rounded and muscular. The intestinal caecum is simple, bifurcated, and united posteriorly. There are six pairs of well-developed post-pharyngeal cephalic glands on either side of the bifurcation of the intestinal caeca. Reproductive glands are located on both sides of the seminal vesicle at the level of the copulatory complex.