Phylogenetic Position and Morphology of Spirotrichosomidae (Parabasalia): New Evidence from Leptospironympha of Cryptocercus punctulatus

Parabasalia are a large, diverse clade of anaerobic flagellates, many of which inhabit the guts of wood-feeding insects. Because most are uncultivable, molecular data representing the true diversity of Parabasalia only became possible with the application of single-cell techniques, but in the last decade molecular data have accumulated rapidly. Within the Trichonymphida, the most diverse lineage of hypermastigote parabasalids, molecular data are now available from five of the six families, however, one family, the Spirotrichosomidae, has not been sampled at the molecular level, and is very little studied with electron microscopy. Here we examine a representative of Spirotrichosomidae— Leptospironympha of the wood-feeding cockroach Cryptocercus punctulatus— with scanning and transmission electron microscopy, and analyze its small subunit rRNA gene to infer its phylogenetic position. Phylogenetic analyses place Leptospironympha as sister to a clade comprising Eucomonymphidae and Teranymphidae with moderate support. Examination with scanning and transmission electron microscopy reveals new classes of previously undetected symbiotic surface bacteria, a glycocalyx, granular particles on flagella, and putative phagocytosed bacteria. The range of flagellar patterns in Spirotrichosomidae is quite wide, and the possibility that some members may be more closely related to Eucomonymphidae or Teranymphidae is addressed.