The anatomy and ultrastructure of the proboscis in Zonorhynchus-species and implications for phylogenetic relationships within the Eukalyptorhynchia Meixner, 1928 (Platyhelminthes, Rhabdocoela)

The ultrastructural morphology of the proboscis in species of the genus Zon orhynchus Karling, 1952 is investigated. The proboscis epithelia are organi zed in four belts. The apical cone epithelium has intra-epithelial nuclei, and the distal belt of the sheath epithelium is formed by numerous cells la cking a distinct pattern. Multiciliary receptors are lacking. The diversity in ultrastructural data on the proboscis is used to elucidate the phylogen etic relationships within the Cicerinidae and Eukalyptorhynchia. A bipartit e cone epithelium as found in Zonorhynchus-species is a common feature for all eukalyptorhynch species investigated. A syncytial basal cone epithelium is a synapomorphic character for all species except Toia calceformis Brune t, 1973 and Nannorhynchides herdlaensis Karling, 1956. A syncytial proximal belt of the sheath epithelium, and intra-epithelial nucleus(i) in the apic al cone epithelium constitute apomorphic features for species of the genus Zonorhynchus. The absence of multiciliary receptors is regarded as the ples iomorphic state and distinguishes Zonorhynchus-species, I: calceformis and N. herdlaensis from other Eukalyptorhynchia investigated. Cicerina remanei Meixner, 1928, Psammorhynchus tubulipenis Meixner, 1938 and Cytocystis clit ellatus Karling, 1953 have two insunk sensory organs with multiciliary rece ptors. The presence of four epithelial belts in Zonorhynchus-species as in C. remanei, P. tubulipenis and C. clitellatus is considered a shared plesio morphic state within the Eukalyptorhynchia The presence of a third belt in the sheath epithelium is a synapomorphic character of all Koinocystididae, Cystiplanidae and Polycystididae.