ИСТИНА

The common ancestor of cnidarians and bilaterians is assumed to be bilaterally symmetrical animal with two rings of tentacles (labial and marginal) around the elongated blastopore. The ciliary apparatus of bilaterian larvae forming a closed contour around the elongated blastopore recapitulates the labial ring of ciliary tentacles of common cnidarian/bilaterian ancestor. In adults, the larval adoral ciliary field may give rise to ciliary tentacles, while the neurotroch evolves into the ventral ciliary sole. The metameric parapodia of lophotrochozoan are treated as homologies of the marginal ring tentacles. In chordates (resulted from their upside-down inversion) the dorsal neural folds are the homologies of the labial ring tentacles while the ciliary ependyma of the nerve tube corresponds to the ventral neurotroch. Metameric radials of vertebrate paired fins are treated as homologies of the marginal ring tentacles. As the radials of paired fins evolved into tetrapod digits, so it is possible to trace a long-distance homology between cnidarian tentacles and human fingers. In Cambrian arthropods (Radiodonta, Megaheira, etc.) each segment bore a pair of primary biramous limbs. It was composed of flap-like lateral exopod (possible homologous to the labial ring tentacle) and ventral annulated endopod (possible homologous to the marginal ring tentacle). The lateral flaps evolved into the trilobite gills, chelicerate book-gills and book-lungs, crustacean epipodite gills, and insect wings. The endopods gave rise the arthropodia including the secondarily biramous appendages of crustaceans. The limbless condition of cycloneuralians is interpreted as secondarily loss resulted from the burrowing mode of life.