Ground plan of the larval nervous system in phoronids: Evidence from larvae of viviparous phoronid

Evolution and Development. 2017. Vol. 19. No. 4-5. P. 171–189.

Temereva E.

Nervous system organization differs greatly in larvae and adults of many species, but
has nevertheless been traditionally used for phylogenetic studies. In phoronids, the
organization of the larval nervous system depends on the type of development. With
the goal of understanding the ground plan of the nervous system in phoronid larvae, the
development and organization of the larval nervous systemwere studied in a viviparous
phoronid species. The ground plan of the phoronid larval nervous system includes an
apical organ, a continuous nerve tract under the preoral and postoral ciliated bands, and
two lateral nerves extending between the apical organ and the nerve tract. A bilobed
larva with such an organization of the nervous system is suggested to be the primary
larva of the taxonomic group Brachiozoa, which includes the phyla Brachiopoda and
Phoronida. The ground plan of the nervous system of phoronid larvae is similar to that
of the early larvae of annelids and of some deuterostomians. The protostome- and
deuterostome-like features, which are characteristic of many organ systems in
phoronids, were probably inherited by phoronids from the last common bilaterian
ancestor. The information provided here on the ground plan of the larval nervous
system should be useful for future analyses of phoronid phylogeny and evolution.

Keywords: development, Phylogeny, Nervous system, larvae