First data on the organization of the nervous system in juveniles of Novocrania anomala (Brachiopoda, Craniiformea)

Abstract

The organization and development of the nervous system are traditionally used for phylogenetic analysis and may be useful for clarification of evolution and phylogeny of some poor studied groups. One of these groups is brachiopods: most data on their nervous system organization were obtained in 19th century. In this research, antibody staining and confocal laser scanning microscopy were used to study the nervous system of early ontogenetic stages of the brachiopod Novocrania anomala. Although N. anomala adults are thought to lack a supraenteric ganglion, a large supraenteric ganglion exists in N. anomala juveniles with either a trocholophe or a schizolophe. During ontogenesis, the supraenteric ganglion in the juvenile changes its shape: the commissure between the two lobes of the ganglion extends. This commissure possibly gives rise to the main brachial nerve in adults. The supraenteric ganglion gives rise to the cross (transversal) nerves that extend to the accessory brachial nerve, which gives rise to the tentacular nerves. In juveniles with a trocholophe, the accessory brachial nerve gives rise to the frontal and intertentacular nerves of tentacles that form a single row. When the trocholophe transforms into the schizolophe, the second row of tentacles appears and the innervation of the tentacles changes. The intertentacular nerves disappear and the second accessory nerve forms and gives rise to the laterofrontal tentacular nerves of the inner and outer tentacles and to the abfrontal nerves of the inner tentacles. The so-called subenteric ganglion, which was described as a ganglion in N. anomala adults, is represented by a large circumvisceral nerve in N. anomala juveniles.The results suggest that ‘phoronid-like’ non-specialized tentacles may be regarded as the ancestral type of tentacles for brachiopods and probably for all lophophorates. The presence of intertentacular nerves is the ancestral feature of all lophophorates. The transformation of the juvenile supraenteric ganglion into the main brachial nerve of N. anomala adults suggests that research is needed on the development and organization of the supraenteric ganglion and the main brachial nerve in other brachiopods, whose adults have a prominent supraenteric ganglion.