Fig. 3

Development and morphology of Holothuroidea, focus on H. tubulosa. a Spawning female (G, gonopore; E, eggs); b female gonads; c arrested oocyte, note the nucleus in the center; d mature oocyte, note that the nucleus is not visible anymore; e 2-cell stage; f 4-cell stage; g early gastrula and h late gastrula; i early and j late auricularia larvae; k fully developed doliolaria; l early pentactula larva. m Juvenile and n adult (b–i scale bar = 40 μm; j–m scale bar = 100 μm). H, hydropore; HS, hyaline spheres; T, tentacles; P, podia. a, m are modified from [126], b, c, d, e, f, g, h, i, j, k, I, n are original pictures taken in the Annunziata’s laboratory