Ascidian swimming larvae are entirely surrounded by a hyaline extracellular coat, called as tunic or test, on whichnumerous test cells adhere. The functional role played by test cells in larvae of various ascidian species consists indepositing submicroscopic structures known as ornaments and/or substances of proteoglycan nature in the larval testsurface. The deposition of ornaments would render the larval test hydrophilic and thus allow the larvae to swim beingimmersed in sea water. Ultrastructural investigations reported in literature on larvae of Cionidae and Ascididae familieshave not evidenced the presence of ornaments in the swimming larval test. For these Ascididae families it has beenhypothesized that test cells secrete an amorphous substance that would let them to adhere to larval tunic. In order to clarifythe functional role played by test cells of swimming larvae of the Ascididae family, ultrastructural and cytochemicalinvestigations have been carried out on test cells of Ascidia malaca swimming larvae. The ultrastructural observationshave evidenced that these cells are metabolically active and show an amoeboidic behaviour as they mainly adhere to thesurface of the test. Their cytoplasm is characterized by the presence of a Golgi and large granules that gradually emptytheir contents and release the same on the test surface. The cytochemical investigastions carried out at ultrastructural levelhave evidenced that the substances secreted by test cells and deposited on the larval test consisting of glycosaminoglycans.According to the data reported in literature the results of the present investigations confirm that the deposition ofglycosaminoglycans enables the adhesion of test cells on the surface of larval tunic and would render the Ascidia malacalarva hydrophilic and able to swim being immersed in sea water.
|Titolo della pubblicazione ospite||CURRENT MICROSCOPY CONTRIBUTIONS TO ADVANCES IN SCIENCES AND TECHNOLOGY|
|Numero di pagine||6|
|Stato di pubblicazione||Published - 2012|
|Nome||microscopy book series number 5 vol. 1|