Sedentaria, Lamarck, 1818

Weigert, Anne & Bleidorn, Christoph, 2016, Current status of annelid phylogeny, Organisms Diversity & Evolution (New York, N. Y.) 16 (2), pp. 345-362 : 354-355

Sedentaria

Most of the annelid species that have been investigated extensively in various evolutionary developmental studies fall within the clade of Sedentaria. These include the leech Helobdella robusta and the capitellid Capitella teleta (formerly Capitella sp. I ), but there is also some work available for the leech Hirudo medicinalis , the common earthworm Lumbricus terrestris , the serpulids Hydroides elegans and Spirobranchus (formerly Pomatoceros ) lamarcki, and the oligochaete Tubifex tubifex ( Iwasa et al. 2000; Seaver and Shankland 2001; Werbrock et al. 2001; Song et al. 2002; Tessmar-Raible and Arendt 2003; Seaver et al. 2005; Seaver and Kaneshige 2006; Arenas-Mena 2007; Oyama and Shimizu 2007; Weisblat and Kuo 2009; Rivera and Weisblat 2009; Cho et al. 2010; McDougall et al. 2011; Simakov et al. 2013).

As representatives of the Clitellata, members of Helobdella are small freshwater leeches belonging to the Glossiphoniidae , which do not feed on blood from other animals. Due to their small body size and ease of rearing in the laboratory, species of Helobdella became excellent candidates for experimental studies ( Weisblat and Kuo 2009). Investigations of the cleavage and cell lineage patterns in Helobdella are not only key components that aid our understanding of the embryogenesis of other spiralian animal groups, but also of changes in development connected to a transition to a terrestrial life in Annelida, since Clitellata are deeply nested within polychaetes. Moreover, the availability of the whole genome of H. robusta enables comparisons of genome organization and gene content between annelids and other Bilateria ( Simakov et al. 2013).

Other Sedentaria which are currently studied in evo-devo studies are members of the genus Capitella . Their simple body organization, small size, short generation time, and cosmopolitan distribution, in addition to the fully sequenced genome of C. teleta , are important arguments qualifying capitellids as annelid model species. The embryonic and larval development has been described in detail, as well as regenerative abilities, development of the nervous system, segment formation, and genomic organization ( Werbrock et al. 2001; Seaver et al. 2005; Fröbius and Seaver 2006; Seaver and Kaneshige 2006; Frobius et al. 2008; Hill and Savage 2009; Cho et al. 2010; Giani et al. 2011; Seaver et al. 2012; Simakov et al. 2013; Meyer et al. 2015). Moreover, their phylogenetic position could help us to understand the evolution of segmentation within Annelida, with the non-segmented Echiura as their sister taxon. Comparative developmental and gene expression studies in both taxa might shed light on the formation and loss of segments within Annelida.