Evolution and Structure of Neuromuscular Systems in Spiralian Meiofauna

TY - BOOK

T1 - Evolution and Structure of Neuromuscular Systems in Spiralian Meiofauna

AU - Bekkouche, Nicolas Tarik

PY - 2016

Y1 - 2016

N2 - Spiralia is a vast clade of Metazoa comprising large and well-known organisms, e.g., Annelidaand Mollusca, but also many microscopic animals such as Gastrotricha or Gnathifera (including,Rotifera) of the often overlooked meiofauna. To date, the phylogeny and morphology ofSpiralia have been difficult to resolve and understand. The present thesis focuses on spiralianmeiofauna to i) reconstruct the phylogeny of this clade using transcriptomics and placeenigmatic meiofaunal taxa and ii) resolve the morphology of three important taxa, mainlyemploying confocal laser scanning microscopy and immunohistochemistry: the spiralianincertae sedis, Lobatocerebrum, the recently described monospecific phylum Micrognathozoa(Gnathifera), and an early branching Gastrotricha, Diuronotus aspetos.The new spiralian phylogeny reveals with high support that the deepest branches of Spiraliaconsist of meiofaunal representatives, that Gnathifera is the sister group of remaining Spiralia,that Gastrotricha+Platyhelminthes branches off next and that Lobatocerebrum is an Annelida.The morphological surveys of the musculature, nervous system, glands, and ciliation on threephylogenetically distinct taxa yield more insight into their evolution: Lobatocerebrum is anaberrant annelid showing only few common traits with Annelida, yet, our detailed studiesunravel putative resemblances of muscular, nervous and glandular system to previous findingsin annelids. Micrognathozoa shows more resemblances with Rotifera than Gnathostomulida(these three taxa together forming Gnathifera). Furthermore, we could infer possibleplesiomorphic states of Gnathifera such as the paired ventro-lateral nerve chords (shared withmany Spiralia) as well as recover putative Gnathifera apomorphies such as the pharyngealganglion; all adding new information on the evolution of this group. Diuronotus aspetos showsa unique combination of muscular traits not easily traceable, but in contrast the nervoussystem traits can be compared in high details, hereby bridging to other Chaetonotida(Gastrotricha). Moreover, we describe new gastrotrich characters such as the ciliary pattern ora system of pharyngeal canals of possible importance for future comparative approaches.These different studies show that information on rare and phylogenetically isolated animalswith their unique combination of neural and muscular characters are necessary to understandthe evolution of Spiralia. Also, several organ systems should be considered for systematiccomparisons, here emphasized with ciliary and glandular systems in Micrognathozoa,Gastrotricha and Lobatocerebrum showing potential phylogenetic information.

AB - Spiralia is a vast clade of Metazoa comprising large and well-known organisms, e.g., Annelidaand Mollusca, but also many microscopic animals such as Gastrotricha or Gnathifera (including,Rotifera) of the often overlooked meiofauna. To date, the phylogeny and morphology ofSpiralia have been difficult to resolve and understand. The present thesis focuses on spiralianmeiofauna to i) reconstruct the phylogeny of this clade using transcriptomics and placeenigmatic meiofaunal taxa and ii) resolve the morphology of three important taxa, mainlyemploying confocal laser scanning microscopy and immunohistochemistry: the spiralianincertae sedis, Lobatocerebrum, the recently described monospecific phylum Micrognathozoa(Gnathifera), and an early branching Gastrotricha, Diuronotus aspetos.The new spiralian phylogeny reveals with high support that the deepest branches of Spiraliaconsist of meiofaunal representatives, that Gnathifera is the sister group of remaining Spiralia,that Gastrotricha+Platyhelminthes branches off next and that Lobatocerebrum is an Annelida.The morphological surveys of the musculature, nervous system, glands, and ciliation on threephylogenetically distinct taxa yield more insight into their evolution: Lobatocerebrum is anaberrant annelid showing only few common traits with Annelida, yet, our detailed studiesunravel putative resemblances of muscular, nervous and glandular system to previous findingsin annelids. Micrognathozoa shows more resemblances with Rotifera than Gnathostomulida(these three taxa together forming Gnathifera). Furthermore, we could infer possibleplesiomorphic states of Gnathifera such as the paired ventro-lateral nerve chords (shared withmany Spiralia) as well as recover putative Gnathifera apomorphies such as the pharyngealganglion; all adding new information on the evolution of this group. Diuronotus aspetos showsa unique combination of muscular traits not easily traceable, but in contrast the nervoussystem traits can be compared in high details, hereby bridging to other Chaetonotida(Gastrotricha). Moreover, we describe new gastrotrich characters such as the ciliary pattern ora system of pharyngeal canals of possible importance for future comparative approaches.These different studies show that information on rare and phylogenetically isolated animalswith their unique combination of neural and muscular characters are necessary to understandthe evolution of Spiralia. Also, several organ systems should be considered for systematiccomparisons, here emphasized with ciliary and glandular systems in Micrognathozoa,Gastrotricha and Lobatocerebrum showing potential phylogenetic information.

UR - http://rex.kb.dk/KGL:KGL:KGL01009261866

M3 - Ph.D. thesis

BT - Evolution and Structure of Neuromuscular Systems in Spiralian Meiofauna

PB - Department of Biology, Faculty of Science, University of Copenhagen

ER -