The ascidian phagocyte: a multitasking cell

Ascidians are invertebrate chordates closely related to vertebrates and widely distributed in shallow waters of all the seas and oceans. As invertebrates, they rely on innate immunity for their defence and circulating immunocytes are the effectors of their cell-mediated immune responses. Ascidian immunocytes include phagocytes and cytotoxic, pro-inflammatory cells. The current review focuses on the ascidian phagocyte. By mining the available literature, the functions of this haemocyte-type in organismal biology are reported. The resulting overall picture is that of a cell-type with a clear importance in immunosurveillance, exerted in multiple ways through phylogenetically conserved activation pathways, playing key roles also in other biological processes, such as development.