SABELLARIIDAE AND ITS POSITION

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 : 246

MONOPHYLY OF SABELLARIIDAE AND ITS POSITION

ON THE ANNELID TREE

Even though the monophyly of Sabellariidae has not been tested in a phylogenetic context, several notable features, such as the presence of the operculum bearing rows of paleae derived from the first two segments, the presence of the tentacular filaments on the operculum, the division of the body into four regions, and the arrangement of chaetae, common in all members of the group, have indicated its monophyly over the years. In contrast, the position and sister-group relationships of Sabellariidae with other polychaetes are still obscure ( Rouse & Pleijel, 2003) and different studies have indicated its inclusion within Sabellida , Spionida , or Terebellida .

The group was initially grouped with Sabellidae and Serpulidae ( Levinsen, 1883; Meyer, 1888; Hatschek, 1893; Benham, 1896) because of the arrangement of thoracic nephridial pores and the interpretation of the food-collecting organs of these three families as homologous. This relationship was also justified latterly by the chaetal inversion in the abdominal region ( Knight-Jones, 1981; Fitzhugh, 1989; Rouse & Fauchald, 1997) and the innervation of the palps ( Orrhage & Müller, 2005). But other studies indicated that the tentacular filaments and palps in sabellariids and radiolar crown in sabellids and serpulids have a different origin ( Orrhage, 1978; Orrhage & Müller, 2005) and therefore they should not be considered as homologous. Recently, the chaetal arrangement in Sabellariidae has also been suggested as being not homologous to the sabellid– serpulid chaetal inversion pattern ( Kieselbach & Hausen, 2008), providing no support for a sistergroup relationship of sabellids and sabellariids. Concurrently, a phylogenetic hypothesis combining morphological and molecular data has also indicated that Sabellariidae and Sabellida (including Sabellidae and Serpulidae ) are not closely related ( Rousset et al., 2004; Zrzavý et al., 2009; Capa et al., 2011).

Sabellariids have also been thought to be related to spionids ( Meyer, 1888; Caullery, 1914). A revealing study by Dales (1962) places sabellariids within Spionida based on larval morphology and palp innervation. This relationship has also been recently suggested, after comprehensive analyses of combined morphological and molecular data ( Rousset et al., 2004; Capa et al., 2011), as well as behavioural and ecophysical investigations ( Amieva & Reed, 1987; Dubois et al., 2005).

Other authors have considered sabellariids as related to Terebellida ( Savigny, 1822; Fauchald, 1977) or Terebelliformia (sensu Rouse & Pleijel, 2001), because of the presence of buccal tentacles (referred to tentacular filaments herein), and similarities regarding larval metamorphosis and opercular structure between sabellariids and pectinariids have been suggested ( Rouse & Pleijel, 2001). The homology between the opercular structures has still to be tested ( Orrhage, 2001; Bartolomaeus, Purschke & Hausen, 2005).