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 : 270-271

SABELLARIIDAE RELATIONSHIPS AND

CHARACTER EVOLUTION

The topologies of the unweighted characters, resulting in a consensus tree where only few clades are delineated, indicate the high amount of homoplasy accumulated in the group. A close relationship of Idanthyrsus and Lygdamis , previously considered as members of Sabellariinae and Lygdaminae ( Kirtley, 1994), respectively, recovered in both the unweighted and the implied weighted datasets suggest these subfamilies are not monophyletic, and therefore this classification should be avoided.

The implied weighting did resolve the polytomies and uncertain relationships within Sabellariidae (for other examples and discussion of the methodology, see Goloboff, 1993, Goloboff et al., 2008a; Ramírez, 2003). But different results are reached depending on the value given to the concavity constant. Only the groups presented in all concavities explored should be considered as firmly established ( Goloboff et al., 2008a) and therefore the basal relationships among those members of ‘Clade A’ should considered as unresolved for now.

Major morphological differences among members of Sabellariidae are found in the anterior end, probably due to major adaptative variations in morphology and anatomical structure, resulted as a consequence of external applied stress caused by environmental conditions or biological interactions ( Kirtley, 1994). In contrast, the posterior segments are similar in all genera and species. The number of parathoracic segments justified the erection of the two subfamilies ( Kirtley, 1994), a criterion that seemed justified because this is established very early in the course of development ( Bhaud & Fernández-Álamo, 2001). However, we advocate that the number of parathoracic segments is homoplastic with four segments being the plesiomorphic condition and changing to three twice during the sabellariid radiation.

The presence of short opercula, geniculate outer paleae, and inner concave paleae arranged in semicircles are apomorphic features that characterize the derived sabellariids ( Bathysabellaria , Gunnarea , Paraidanthyrsus , Sabellaria , Phragmatopoma , Neosabellaria ). Besides, given the lack of a phylogenetic framework, some authors predicted that Phragmatopoma was a derived sabellariid due to their developed paleae ( Dales, 1952) and sperm shape ( Eckelbarger, 1976), compared with other Sabellariidae . The relationship between Phalacrostemma and this group of derived sabellariids is supported by features that are not of much significance such as length of the operculum, limbation of hooks (inapplicable for most taxa), and the presence of chaetae on the neuropodia of segment 1, instead of being grouped with the taxa that show a similar opercular structure and, in our opinion, should be considered with caution.

About 20 species, predominantly of the genera Phragmatopoma , Sabellaria , and including the monospecific genus Gunnerea, construct colonies and reefs of aggregated tubes in the intertidal and subtidal zones of temperate and tropical coasts in many parts of the world ( Achari, 1974; Kirtley, 1974; Pawlik, 1988a, b; Pawlik & Faulkner, 1988). After the phylogenetic hypothesis presented herein we can conclude that this characteristic and the bathymetric restrictions of some of the taxa seem not to have any phylogenetic constraint.

This paper represents the first comprehensive systematic revision of the family. Combined morphological and molecular data confirm the monophyly of Sabellariidae and its close relationships with Spionida . Phylogenetic relationships within Sabellariidae have been assessed using morphological data and suggest that the established sabellariid subfamilies are not monophyletic and the proposed groups are now based on opercular and chaetal features. The descriptions of morphological features together with the illustrations will, we hope, be used as a baseline for further systematic and taxonomic studies in the group, many species of which remain poorly described.