Ontogenetic divergence in the phytoparasitic nematodes Macroposthonia nainitalensis and M. tenuiannulata (Criconematidae, Tylenchia)

Promorphogenesis, egg cleavage, and gastrulation proceed in Macroposthonia nainitalensis similarly to other phytonematodes of the subclass Tylenchia. Before the onset of gastrulation, the greatest similarity was observed in a descendant of the micromere 2b, which separates macromeres of the third division. Deviations from the general line of development started in this species during embryonal organogenesis with the formation of an external epithelium with a special rough surface layer, which was absent in the embryos of other phytonematodes. In addition, during this period of acceleration, the digestive system developed, while peristaltic changes in body shape appeared at the tadpole stage. Later, somatic muscle development was enhanced in the first instar larvae of M. nainitalensis, while in the second instar larvae of Macroposthonia spp. somatic muscle cells were located at an acute angle to the longitudinal body axis. In addition, denticles--microchaetae appeared in the second to fifth instar larvae of these nematodes. All these features, which have not been observed in other phytonematodes of the subclass Tylenchia, help the peristaltic crawling of Macroposthonia spp. In contrast to other Tylenchia, the musculocutaneous sac did not develop in Macroposthonia spp. However, there are similarities in the development of the digestive and genital systems.