Allopseudaxine yaito is a species of monogenean flatworm, which is parasitic on the gills of a marine fish.

The digestive organs include an anterior mouth, a pharynx, an oesophagus and a posterior intestine that bifurcates at about the level of genital pore in two lateral branches.

The intestinal branches terminate at posterior end of body proper, the left limb extends along the haptor and reaches the lappet.

The reproductive organs include an anterior genital atrium armed with a crown of 13 hooks, a cirrus bulbous projecting into genital atrium, armed with a crown of slender spines, one row of ventrosubmarginal vaginae on each side of the body, each row divided into a longitudinal row of transverse slit-like areolae with heavily cuticularized margins, and each row is connected with the reticular vitelline ducts of its own side, an ovary, and 40-65 large testes pre, para and post-ovarian.

[1] The type-host is the kawakawa or mackerel tuna Euthynnus affinis (Scombridae).