May play a role in sequestering potentially toxic fatty acids and their peroxidation products, or it may be involved in the maintenance of the impermeable lipid layer of the eggshell. Abundant in the fluid surrounding the developing embryo of Ascaris suum. Synthesis appears to be switched off shortly after hatching from the egg and invasion of the host. P18 is not found in unembryonated eggs, begins to be synthesized at about day 3 of development, reaches a maximal concentration with the formation of the first-stage larva and remains abundant in the perivitelline fluid of the second-stage larva. Forms a beta-barrel structure that accommodates hydrophobic ligands in its interior. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family.