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

Abstract

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.