Morphology of four different larvae of Nematodes inclusive of Anisakis type (Filocapsularia) was studied. Larvae were collected from Trachurus japonicus on which they live as parasites. These larvae were classified by the method of Skrjabin et al, and they were found to be larvae of Raphidascaris, Anisakis (Filocapsularia), Contracaecum, and Amplicaecum. Both light and electron microscope observations were carried out with cross-section specimens of these larvae, and it was possible to obtain some characteristic morphological features of the larvae of Anisakis type. Some of these features that differ from those of other larvae are described briefly in the following.
1. The length of larvae of Anisakis type is longest of all the four kinds, and the cross-section of this larva revealed a lateral cord which has a peculiar shape and size.
2. This larva has the thickest cuticle as compared with other three kinds, and the number of muscle cells is most numerous. In addition, the arrangement of the bond of myofibrils is characteristic.