Ultrastructure of Diophrys appendiculata and new systematic consideration of the euplotid family Uronychiidae(Protista,Ciliophora)

The ultrastructure of ciliates carries important cytological,taxonomical,and evolutionary signals for these single-celled eukaryotic organisms.However,little ultrastructural data have been accumulated for most ciliate groups with systematic problems.In the present work,a well-known marine uronychiid,Diophrys appendiculata,was investigated using electron microscopy and a comparison with,and a discussion considering,phylogenetic analyses were made.The new findings primarily show that:(i)this species lacks the typical alveolar plate,bears cortical ampule-like extrusomes,and has microtubular triads in the dorsal pellicle,and thus exhibits some ultrastructural features in common with most of its previously studied congeners;(ii)each adoral membranelle before the level of frontal cirrus II/2 contains three rows of kinetosomes and each membranelle after the level of frontal cirrus II/2 contains four rows,which might be related with morphogenesis and could be considered as a distinctive character of Diophrys;(iii)some structural details of the buccal field,such as the extra-pellicular fibrils,pellicle,pharyngeal disks and microtubular sheet,were documented.In addition,based on the ultrastructural comparison of representatives,we discuss the differentiation between the subfamilies Diophryinae and Uronychiinae.A hypothetical systematic relationship of members in the order Euplotida based on a wide range of data is also provided.