The digestive system of xenacoelomorphs

Abstract

Interest in the study of Xenacoelomorpha has recently been revived due to realization of its key phylogenetic position as the putative sister group of the remaining Bilateria. Phylogenomic studies have attracted the attention of researchers interested in the evolution of animals and the origin of novelties. However, it is clear that a proper understanding of novelties can only be gained in the context of thorough descriptions of the anatomy of the different members of this phylum. A considerable literature, based mainly on conventional histological techniques, describes different aspects of xenacoelomorphs' tissue architecture. However, the focus has been somewhat uneven; some tissues, such as the neuro-muscular system, are relatively well described in most groups, whereas others, including the digestive system, are only poorly understood. Our lack of knowledge of the xenacoelomorph digestive system is exacerbated by the assumption that, at least in Acoela, which possess a syncytial gut, the digestive system is a derived and specialized tissue with little bearing on what is observed in other bilaterian animals. Here, we try to remedy this lack of attention by revisiting the different studies of the xenacoelomorph digestive system, and we discuss the diversity present in the light of new evolutionary knowledge.

Transgenesis in the acoel worm Hofstenia miamia

“…Fig. 1), consistent with the presence of a syncytial digestive system, which has been reported for some acoels (Smith, 1981;Gavilán et al, 2019). Shortly after hatching, we sorted G0 animals based on the presence of transgene expression and the intensity of fluorescence: only those exhibiting strong fluorescence and the largest area of expression were raised to adulthood and screened regularly for continued transgene expression.…”

Evolution and Comparative Physiology of Luqin-Type Neuropeptide Signaling

“…The phylum Xenacoelomorpha comprises an assemblage of marine worms that have a simple body plan without a throughgut (Hejnol and Pang, 2016;Telford and Copley, 2016;Gavilán et al, 2019). They are of particular interest for evolutionary studies because of controversy regarding their phylogenetic position in the animal kingdom.…”

Structure, development and evolution of the digestive system

“…Molecular-genetic studies have revealed important themes in gut development, and several reviews of the special issue summarize the current knowledge in this area [Annunziata et al 2019 Contrasting with a strongly conserved repertoire of genetic mechanisms acting in gut development is the evident diversity of the architectures and cellular compositions of the digestive systems, which results from the need to adapt to the different types of food that animals consume. Examples of gut diversity surveyed in detail in this special issue include the sponges (Godefroy et al 2019), acoels (Gavilán et al 2019) and molluscs (Lobo-da-Cunha 2019).…”