Ultrastructural comparative analysis on the adhesive papillae of the swimming larvae of three ascidian species

This paper presents a preliminary report on the papillae of the swimming larvae of three ascidian species: Ascidia malaca, Phallusia mammillata and Ciona intestinalis. The investigations, carried out at ultrastructural level and at confocal laser microscope, have evidenced, in the adhesive papillae of the three studied species, three different cell-types: axial columnar cells, collocytes, sensory cells respectively. The adhesive papillae of A. malaca and P. mammillata show central axial columnar cells with long microvilli emerging from the apical edge and extending throughout the hyaline cap. Collocytes are elongated secreting cells, lying in middle-lateral side. Sensory cells have a cilium at the apical side and an axon proceeding from the basal side. The adhesive papillae of C. intestinalis present some differences in the ultrastructure of the axial columnar cells, which bear a big digitiform protrusion, extending throughout the hyaline cap and a lot of microtubules along the cell axis. The investigations, carried out at confocal microscopy, have evidentiated a clear fluorescence in the papillae of the three studied species and a network of nervous fibers projecting from the papillar base up to cerebral vesicle of the cephalenteron. The characteristic of simple and coniforme type and the adhesive and sensorial functions of adhesive papillae of three ascidian species examined are confirmed.