Redescription and embryonic developmental dynamics of Aphelenchoides bicaudatus with implications for nematode...

Aphelenchoides bicaudatus is widely reported yet frequently confused with morphologically similar congeners. We redescribe A. bicaudatus recovered from declining Pinus massoniana and associated Monochamus alternatus in eastern China using integrated light microscopy, SEM, and rDNA markers (ITS and SSU). Key diagnostic characters, particularly the bifurcated female tail terminus and SEM-resolved lip annulation, matched prior descriptions and were supported by congruent maximum-likelihood phylogenetic placement with reference sequences. We further document embryogenesis under controlled conditions and provide a time-resolved staging series from oviposition to hatching (approximately 60 h) in a parthenogenetic line, highlighting an extended one-cell phase relative to related aphelenchoids. These data expand the currently limited baseline of developmental information for Aphelenchoides and provide practical morphological and molecular references for identification. Our field sampling records co-occurrence with pine decline and beetles, but does not establish causality or vectoring.