Abstract
Syllidae is one of the most species‐rich groups within Annelida, with a wide variety of reproductive modes and different regenerative processes. Syllids have striking ability to regenerate their body anteriorly and posteriorly, which in many species is redeployed during sexual (schizogamy) and asexual (fission) reproduction. This review summarizes the available data on regeneration in syllids, covering descriptions of regenerative mechanisms in different species as well as regeneration in relation to reproductive modes. Our survey shows that posterior regeneration is widely distributed in syllids, whereas anterior regeneration is limited in most of the species, excepting those reproducing by fission. The latter reproductive mode is well known for a few species belonging to Autolytinae, Eusyllinae, and Syllinae. Patterns of fission areas have been studied in these animals. Deviations of the regular regeneration pattern or aberrant forms such as bifurcated animals or individuals with multiple heads have been reported for several species. Some of these aberrations show a deviation of the bilateral symmetry and antero‐posterior axis, which, interestingly, can also be observed in the regular branching body pattern of some species of syllids.
Highlights
OVERVIEW OF ANNELID REGENERATIONRegeneration is a postembryonic morphogenesis characterized by the ability of an organism to restore lost parts of the body (Bely & Nyberg, 2010; Brockes & Kumar, 2008)
The nervous system at the posterior end of T. antoni regenerates in a similar way, but the blastema is formed in 3 days, and a day after a new pygidium with cirri is present (Weidhase et al, 2017)
During sexual reproduction by schizogamy, syllids regenerate the posterior body after release of a stolon, thereby being able to undergo another stolonization cycle
Summary
Regeneration is a postembryonic morphogenesis characterized by the ability of an organism to restore lost parts of the body (Bely & Nyberg, 2010; Brockes & Kumar, 2008). Several species, such as Pristina leidyi (Bely & Wray, 2001; Özpolat & Bely, 2015; Özpolat et al, 2016; Zattara & Bely, 2011) and E. japonensis (Myohara, Niva, & Lee, 2006; Myohara et al, 1999; Yoshida-Noro, Myohara, Kobari, & Tochinai, 2000), reproduce asexually in a process that involves regeneration Groups such as Eunicida and Syllidae have reproductive modes (schizogamy or stolonization) that include stages of segment regeneration in the posterior body (Aguado, Glasby, Schroeder, Weigert, & Bleidorn, 2015; Aguado, Helm et al, 2015; Franke, 1999; Rouse & Pleijel, 2006) (Figure 2, Table 1). We focus on the regenerative abilities and reproductive modes of syllids, differences between anterior and posterior regeneration, cells and tissues involved, and aberrant forms as a result of anomalous regenerative processes
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