ИСТИНА

1. The most plesiomorphic type of development among the echinoderms is characteristic for Holothuroidea: free-swimming ciliated blastula, free-swimming ciliated gastrula, dipleurula with simple ciliary band (starts feeding), auricularia with intricately arranged ciliary band (actively feeding), larva with simplified ciliary band – doliolaria (non-feeding), metamorphosis. 2. Most of Eleutherozoa (sea stars, sea urchins, and brittle stars) have the following stages in their life cycle: free-swimming ciliated blastula, free-swimming ciliated gastrula, dipleurula with simple ciliary band (starts feeding), feeding larva with intricately arranged ciliary band (bipinnaria, echinopluteus, ophiopluteus), metamorphosis. However, in some sea urchins and brittle stars, the rudimentary doliolaria remained in the development. 3. In the life cycle of modern sea lilies, only the following stages remained: doliolaria (non-feeding), metamorphosis. All stages, which precede doliolaria, are embyonized. 4. The plesiomorphic variant of the life cycle of Enteropneusta includes the following stages: blastula (embryonized), gastrula (embryonized), free-swimming dipleurula (starts feeding), free-living tornaria with intricately arranged ciliary band from Heider's stage to Krohn's stage (actively feeding), free-swimming Spengel's stage with simplified ciliary band (non-feeding), metamorphosis. 5. Thus, there is reason to believe that the life cycle of the common ancestor of Ambulacraria included the following larval stages: free-swimming ciliated blastula, free-swimming ciliated gastrula, dipleurula with simple ciliary band (starts feeding), larva with intricately arranged ciliary band (actively feeding), larva with simplified ciliary band (non-feeding), metamorphosis. In different groups of Ambulacraria, the stages of life cycle were embryonized right up to achieving the direct development. In Asteroidea, Echinoidea, and Ophiuroidea, the stage of non-feeding larva with simplified ciliary band, i.e. doliolaria, is lost.