ИСТИНА

The organization of tentacle apparatus in bilaterians may help to understand the morphology of the last common bilaterian ancestor (LCBA). The main question is if LCBA possessed tentacle apparatus or not. Oweniidae is clade of annelids with “basal radiation”, which might retain some ancestral features of the LCBA. The organization of tentacles of Owenia borealis is studied by CLSM, SEM, TEM, and 3D reconstructions. The tentacle apparatus consists of 4 pairs of arms, which are located laterally and divided to left and right groups by indistinct dorsal ridge and ventral pharyngeal organ. The letter consists of two parts: the dorsal lip and the ventral pouch, which contains the inner cavity and has a different organization of the ventral and the dorsal epithelium. The pharyngeal organ is surrounded by ventro-lateral lips. Oral side of tentacles and ventro-lateral lips are covered by numerous cilia, whereas the pharyngeal organ lacks of cilia. There are two nerve rings: inner and outer. Each arm is innervated by six thick nerves and many thin neurites, which start from the outer nerve ring. The coelomic lining of tentacle is formed by specialized coelothelium and myoepithelial monociliated cells. The specificity of tentacles organization i.e. the absence of specialized zones along tentacle, independent innervation of tentacles, the histological simplicity of coelomic lining and nerve rings in O. borealis may be evidence of the ancestral state or unspecialized tentacle apparatus, which was used for food particles collection, how the LCBA probably did. The Russian Science Foundation supports this study (#18-14-00082).