TABLE 1.

Main undifferentiated and differentiated cytotypes involved in invertebrate deuterostome regeneration.

Phylum	Clade	Phenomenon	Progenitor cells	Cells undergoing dedifferentiation
Echinodermata	Crinoidea	Arm and visceral mass regeneration	Amebocytes, coelomocytes	Muscle cells, coelomic epithelium, neurosecretory cells
	Echinoidea	Spine and test regeneration -	-	Muscle cells, sclerocytes
	Asteroidea	Arm regeneration	Coelomocytes	Muscle cells, coelomic epithelium
	Ophiuroidea	-	-	Muscle cells, coelomic epithelium
	Holothuroidea	-	-	Muscle cells, coelomic epithelium, glial cells
Hemichordata	Enteropneusta	Anterior and posterior regeneration	Circulating stem cells associated with blood vessels (?), mesenchymal cells (?)	Unclear
Cephalochordata	Leptocardii	Tail regeneration	Muscle satellite-like cells (?) in the tail; coelomocytes (?), mesenchymal cells (?) in oral cirri	Muscle cells (?), nerve cord cells (?), notochord cells (?) in the tail; skeletal rod cells in oral cirri (?)
Tunicata	Ascidiacea	Short distance partial body regeneration Long distance partial body regeneration Blastogenetic regeneration CCS regeneration WBR	ASCs in the oral siphon of Ciona, Cells from the peripharyngeal stem cell niches Bud tissues Vascular epithelium Hemoblasts	Bud tissues Vascular Epithelium Hemoblasts

Terms and Definitions: Blastema, Localized pool of cells, undifferentiated/pluripotent as well as retaining their tissue origin, usually of mesenchymal origin and enveloped by an epithelial layer, able to massively proliferate and differentiate into different cytotypes; Dedifferentiation, Process of cellular reprogramming by which differentiated (mature) somatic cells lose their specialization (oligo/unipotency) and revert to a less differentiated state (pluri/multipotency); Deuterostomes, Eumetazoans that during embryonic development show radial indeterminate cleavage and enterocoely, with the blastopore becoming the anus; Epithelial-Mesenchymal Transition, Dynamic and finely regulated process during which epithelial cells lose their epithelial features, disrupt their underlying basement membrane and assume features typical of mesenchymal cells, such as migratory capacity and production of extracellular matrix components. It is typical of embryonic development, tissue regeneration and morphogenesis, cancer invasion, wound healing, immune response, etc; Epimorphosis, Regeneration model mainly based on the proliferation and differentiation of cells composing the localized blastema; Morphallaxis, Regeneration model mainly based on the remodeling of pre-existing tissues without the formation of a localized blastema through significant local cell proliferation. It may involve the dedifferentiation of localized tissues or migration of cells from other distant locations; Progenitor Cells, Stem cell-derived cells lacking unlimited self-renewal capacity, and that differentiate into limited specialized cytotypes; Transdifferentiation, Process of cellular reprograming by which differentiated (mature) somatic cells convert directly into another type of differentiated (mature) somatic cell without passing through an intermediate pluripotent/multipotent state.