Cuticular changes and structural dynamics in the fourth-stage larvae and adults of Ascaris suum Goeze, 1782 (Nematoda: Ascaridoidea) developing in swine

Abstract

Fourth-stage larvae and adults of Ascaris suum recovered from pigs at 11 days after infection (DAI) to maturity were examined by light and scanning electron microscopy for changes in the cuticle. Allometric body growth in the larva affects the structure of the cuticle in three ways. First, there is increasing separation of the external striae and incomplete longitudinal ridges which closely follows the longitudinal and circumferential expansion of the body. Second, although the cuticle increases in absolute thickness, its thickness in relation to the midbody diameter decreases. Third, the spiral fibre system in the basal layer is elongated, causing a decrease in the spiral angle. All three of these changes are the reverse of that which occurs in the adult cuticle after the fourth moult at 22 DAI. An analysis of the structural dynamics of the larval cuticle shows the decreased spiral angle to be approaching the functional limit of a hydrostatic skeleton enclosed within an anisometric exoskeleton.