BUCCAL CAPSULE DEVELOPMENT AS A CONSIDERATION FOR PHYLOGENETIC ANALYSIS OF RHABDITIDA (NEMATA)

Bacterial feeding nematodes in the order Rhabditida including Zeldia p unctata (Cephalobidae) and Caenorhabditis elegans (Rhabditidae) differ profoundly in the buccal capsule parts and associated cells. We carri ed out a range of tests to determine which buccal capsule parts and ce lls are evolutionarily homologous between the representative species o f the two families. Tests included reconstruction of the buccal capsul e and procorpus with transmission electron microscopy (TEM), nuclei po sition and morphology using 4,6-diamidino-2phenylindole (DAPI) stainin g, and cell lineage using four dimensional (4D) microscopy. The lining of the buccal capsule of Z. punctata and additional Cephalobidae incl udes four sets of muscular radial cells, ma, mb, me and md, in contras t to C. elegans and additional Rhabditidae, which has two sets of epit helial cells (el, e3) and two sets of muscle cells (ml, m2). Cell line age of a nematode closely related to Z. punctata, Cephalobus cubaensis , supports the hypothesis that in cephalobids the el and e3 cells beco me hypodermal cells or are programmed to die. Our findings contradict all previous hypotheses of buccal capsule homology, and suggest instea d that ma and mb in Z. punctata are homologous to mi and m2 in C. eleg ans respectively. We also hypothesize that ma and mb could be homologo us to primary and secondary sets of stylet-protractor muscle cells in the plant parasitic Tylenchida.