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

Abstract

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 system were 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.

The ultrastructure of the apical organ of the Müller's larva of the tiger flatworm Prostheceraeus crozieri

“…In phoronid larvae (actinotrochs), the presence of an apical organ and a frontal organ has been reported (Lacalli, 1990; Temereva, 2017). Both these organs in actinotrochs show limited similarity to the frontal or apical organs of molluscs, entoprocts, and platyhelminths (Temereva & Tsitrin, 2014).…”

“…Both these organs in actinotrochs show limited similarity to the frontal or apical organs of molluscs, entoprocts, and platyhelminths (Temereva & Tsitrin, 2014). The frontal organ of actinotrochs, also called the pyriform organ, is unciliated, of sensory character and in serval species, is not outwardly visible (Temereva, 2017; Temereva & Tsitrin, 2014). In ectoproct larvae, a similar frontal/pyriform organ also exists in addition to an apical organ (formed of monociliated cells).…”

“Noah’s Ark” Project: Interim Results and Outlook for Classic Collection Development

“…The studies in the "Animals" section are aimed at analyzing key aspects of BD on the basis of an integrated approach combining phylogenomic and phylo- The macrotaxonomic analysis of the main Animalia groups included taxa ranging from order to phylum. One fundamentally new finding is the reliable substantiation of the monophiletic status of the Lophophorata clade including Phoronida, Brachiopoda, and Bryozoa: it is supported by the architecture of the coelomic system and innervation of lophophore tentacles [2][3][4][5][6][7][8][9]. This conclusion is of crucial importance for elucidating the structure of the phylogeny of animals at the level of the Metazoan basal radiation.…”

“Noah’s Ark” Project: Interim Results and Outlook for Classic Collection Development

“…The macrotaxonomic analysis of the main Animalia groups included taxa ranging from order to phylum. One fundamentally new finding is the reliable substantiation of the monophiletic status of the Lophophorata clade including Phoronida, Brachiopoda, and Bryozoa: it is supported by the architecture of the coelomic system and innervation of lophophore tentacles [2-9]. This conclusion is of crucial importance for elucidating the structure of the phylogeny of animals at the level of the Metazoan basal radiation.…”