SABELLARIIDAE, , Kirtley, 1994

Capa, María, Hutchings, Pat & Peart, Rachael, 2012, Systematic revision of Sabellariidae (Polychaeta) and their relationships with other polychaetes using morphological and DNA sequence data, Zoological Journal of the Linnean Society 164 (2), pp. 245-284 : 269-270

POSITION OF SABELLARIIDAE

The monophyly of Sabellariidae , even before tested in a phylogenetic framework, has never been questioned as the group presents several morphological and developmental features unique and common to all of its members. However, its position among the annelid tree and the relationships within the family are still far from being understood. For our analyses we included available DNA information of common markers used for resolving deep-level relationships and in combination with a broad range of morphological data. Results suggest that Sabellariidae is closely related to Spionida , although support for this sister-group relationship is weak. Other authors have also reached similar conclusions when combining morphological and molecular data regardless of the markers used ( Rousset et al., 2004; Capa et al., 2011) and also after performing ecophysiological investigations ( Amieva & Reed, 1987; Dubois et al., 2005). The organization and structure of tentacular filaments and the organization of cilia on tentacles have suggested Sabellariids to be closer to Spionids and Terebellids than Sabellids ( Dubois et al., 2005). Our hypothesis also suggests that Spionida is polyphyletic (as in Rousset et al., 2004) with Magelona recovered as closely related to Cirratulidae . The monophyly of Terebellida could also not been assessed as Pectinariidae and Oweniidae were found as sister groups. These results suggest, as in many other studies trying to address basal relationships in Annelida (e.g. Struck & Purschke, 2005; Rousset et al., 2007, Zrzavý et al., 2009), that further investigations should probably consider other markers that enlighten the explosive radiation of this group of metazoans.

If Sabellariidae is not closely related to Sabellida , the idea of the common origin of ‘crown’ structures and arrangement of chaetae in thoracic and abdominal segments ( Rouse & Fauchald, 1997) is discarded (as Kieselbach & Hausen, 2008). It would also mean that the scaphe and cauda, the opercular structure ( Hartman, 1944; Rouse & Pleijel, 2001), and the building organ ( Rousset et al., 2004) are not homologous (as in Watson, 1928). If Terebellida and Sabellariidae are also not closely related, the head structures and the tentacles in terebellids and sabellariids also have different origins.

The suggestion that Sabellariidae is one of the most specialized groups of polychaetes ( Dales, 1952) is defended herein. If the sister-group relationships with Spionidae are confirmed, that would mean that the tubiculous ancestor of this group of worms developed a complex operculum with paleae from some anterior segments that allowed them to live permanently in a tube and with associated feeding structures, such as tentacular filaments for collecting floating particles and the building organ as a specialized structure for cementing these particles with secreted gluing substances. A regionalization of the body also took place and noto-, neuropodia and associated chaetae suffered dramatic changes with respect to preceding forms.