The number of moults in the egg of sealworm, Pseudoterranova decipiens (Nematoda: Ascaridoidea): an ultrastructural study

Abstract

The number of moults in the egg of sealworm, Pseudoterranova decipiens (Nematoda: Ascaridoidea), and other ascaridoids is contentious. Transmission electron microscopic analysis of eggs and free-living larvae of sealworm confirmed that only one moult occurs in the egg. The first-stage larval (L1) cuticle on embryos was first observed in eggs incubated at 15 °C in sea water on day 5 after eggs were dissected from the uterus of sealworm obtained from the stomach of grey seals. There was no ecdysis of this L1 cuticle. A second cuticle began to form beneath the L1 cuticle between day 5 and 12. The second-stage larval (L2) cuticle continued to develop and on day 12 the L2 larva hatched enclosed within the cuticle of the first stage. The L1 cuticle appeared to be partially resorbed during development of the L2 cuticle. This study provides the first ultrastructural evidence of the number of moults that occur in eggs of sealworm.