The Early Embryonic-Development of the Mnesarchaeid Moth, Mnesarchaea-Fusilella Walker (Lepidoptera, Mnesarchaeidae), and Its Phylogenetic Significance

Abstract

Formative processes of the blastoderm, germ disk, germ rudiment and embryonic membranes in the mnesarchaeid moth, Mnesarchaea fusilella, are described, and their phylogenetic significance is discussed. The egg is ovoid, about 0.32 mm by 0.48 mm in size. Below the thin chorion lies a very thick vitelline membrane. In the newly laid eggs, this membrane is colourless, but it becomes blackly pigmented about 30 hours after oviposition. Soon after the completion of the blastoderm, the germ disk or embryonic area forms in the posteroventral region of the egg. It then invaginates into the yolk, and becomes a sac-shaped germ rudiment. After closure of its opening, the germ rudiment separates from the rudimentary serosal or extra-embryonic area Its inner region later develops into the embryo, and its outer one into the amnion. The serosa is thick and each of its cells has two nuclei. The formative process of the germ rudiment and embryonic membranes in M. fusilella is primitive and very similar to that of the hepialid moths, Endoclita excrescens and E. sinensis. From the embryological standpoint, Mnesarchaea clearly belong to the Exoporia because of the following two synapomorphic characters: (1) formation of the thick, blackly pigmented vitelline membrane: and (2) presence of thick, bi-nucleated serosal cells.