Flabelliforma montana (Phylum Microsporidia) from Phlebotomus ariasi (Diptera, Psychodidae): ultrastructural observations and phylogenetic relationships

Ultrastructural observations are presented on Flabelliforma montana (type s pecies) (Phylum Microsporidia) from sandflies Phlebotomus ariasi (Diptera, Psychodidae). Ail stages have isolated nuclei. The sporophorous vesicle (SV ) arises by separation of a 5 nm layer, via small blisters, from the 15 nm surface membrane of sporonts. Sporoblasts form by deep invagination of the sporont surface, the SV at first folding inwards around the invaginations b ut later unfolding to form a rounded vesicle enclosing spores. The vesicle contains tubules with bulbous terminal expansions. Spores have a deeply dom ed anchoring disc within a polar sac which covers the anterior polaroplast, consisting of membranes acutely angled to the longitudinal axis around the straight section of the polar tube. Posterior polaroplast membranes, in th e region where the polar tube changes course towards the periphery, appear almost transverse in sagittal section. The 130 nm thick endospore is overla in by several membrane-like layers, which together with amorphous material constitute the exospore. There are 3.5-4.0 coils of the polar tube. Flabell iforma ostracodae, Flabelliforma diaptomi and Flabelliforma magnivora confo rm well in morphology with the type species. However, when F. magnivora was included in parsimony and maximum likelihood analyses, using 16S rDNA sequ ences of 20 microsporidia, it emerged as unrelated to F. montana. Dispariti es were found between morphological characters and molecular groupings of s everal of the microsporidia investigated. Within clades, nuclei could be is olated or diplokaryotic, sporophorous vesicles present or absent and life c ycles simple or complex.