The internal anatomy and histology of the deutonymph of the fish mite Lardoglyphus konoi are described from paraffin sections viewed under immersion lens. The deutonymph has well developed body wall, muscular system, digestive system and nervous system. Sexes cannot be distinguished in the deutonymph because the genital organs are in their rudiments. Mouth and anal opening and specialised cells in the epithelium of the stomach, caeca and rectum indicate a functional state of the alimentary canal. The epithelium of the anterior part of the caeca contains characteristic spherules. The nervous system consists of the supra-oesaphageal ganglion, circum-oesophageal connectives and a ventral cord. But for a faint demarcation into right and left lobes, separate lobes, centres or tracts are not discernable in the brain. The ventral cord has five separate clusters of cells on the ventral surface of which the anteriormost is the sub oesophageal ganglion and the rest the segmental ganglia. A pair of cylindrical ridges formed of ground protoplasm containing rows of nuclei form the genital rudiments.