Key novelties in the evolution of the aquatic colonial phylum Bryozoa: evidence from soft body morphology

Thomas Schwaha, Andrew N. Ostrovsky, Andreas Wanninger

Результат исследований: Научные публикации в периодических изданияхстатья

1 Цитирования (Scopus)

Аннотация

Molecular techniques are currently the leading tools for reconstructing phylogenetic relationships, but our understanding of ancestral, plesiomorphic and apomorphic characters requires the study of the morphology of extant forms for testing these phylogenies and for reconstructing character evolution. This review highlights the potential of soft body morphology for inferring evolution and phylogeny of the lophotrochozoan phylum Bryozoa (Ectoprocta). This almost exclusively colonial taxon comprises aquatic coelomate filter-feeders that dominate many benthic communities, both marine and freshwater. Despite of a similar bauplan, bryozoans are morphologically very diverse and are represented by three major taxa: Phylactolaemata, Stenolaemata and Gymnolaemata. Recent molecular studies resulted in a comprehensive phylogenetic tree with the Phylactolaemata being sister to the remaining two taxa, and Stenolaemata (Cyclostomata) being sister to Gymnolaemata. We plotted data of soft-tissue morphology onto this phylogeny in order to gain more insight into the evolution of morphological novelties and character evolution in the phylum. All three classes have morphological apomorphies assignable and based on the latest molecular phylogeny, Stenolaemata (Cyclostomata) and Gymnolaemata were united as monophyletic Myolaemata
because of the apomorphic myoepithelial and triradiate pharynx. On of the main
evolutionary changes in bryozoans is a change from a body wall with two welldeveloped muscular layers (as found in other lophotrochozoans) and numerous retractor muscles in Phylactolaemata to a body wall with few specialized muscles and few retractors in the remaining bryozoans. Such a shift probably predated a body wall calcification that independently evolved at least twice in Bryozoa and resulted in evolution of various hydrostatic mechanisms for polypide protrusion. In Cyclostomata, body wall calcification was accompanied by a unique detachment of the peritoneum from the epidermis to form the hydrostatic membraneous sac. The digestive tract of the Myolaemata differs from the phylactolaemate condition. The myolaemate pylorus is ciliated and acts in food transport as well as in faecal pellet formation. Phylactolaemates do not possess a distinguishable pylorus and food manipulation occurs via peristaltic movements of the gut. All bryozoans possess a mesodermal funiculus. A duplication event resulted in an additional anterior/distal funiculus in Gymnolaemata. A colonial system of integration (CSI) of additional, sometimes
branching, funicular cords connecting neighbouring zooids via pores with pore-cell complexes evolved at least twice in Gymnolaemata. Complex communication organs (multiporous septulae) evolved several times in this clade. The nervous system in all bryozoans is subepithelial and concentrated at the lophophoral base and the tentacles. Tentacular nerves seem to emerge intertentacularly in Phylactolaemata whereas they partially emanate directly from the cerebral ganglion or the circum-oral nerve ring in myolaemates. Overall, morphological evidence shows that ancestral forms were small, colonial coelomates with a muscular body wall and a u-shaped gut with ciliary tentacle crown, capable of asexual budding. Coloniality resulted in many noveleites including the origin of zooidal polymorphism, an apomorphic landmark trait of the Myolaemata.
Язык оригиналаанглийский
Число страниц34
ЖурналBiological Reviews
Ранняя дата в режиме онлайн8 янв 2020
DOI
СостояниеЭлектронная публикация перед печатью - 8 янв 2020

    Fingerprint

Предметные области Scopus

  • Биохимия, генетика и молекулярная биология (все)
  • Земледелие и биологические науки (все)

Цитировать